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Trans-Tibial Amputation as a Model to Evaluate the
Role of Cutaneous Sensation, Proprioception and
Muscular Strength on Balance Performance
José Luis Garcia Escorcia, MD
A Thesis
in
The Department
of
Exercise Science
Presented in Partial Fulfillment of the Requirements
for the Degree of Master of Science (Exercise Science) at
Concordia University
Montreal, Quebec, Canada
January 2015
© Jose Luis Garcia Escorcia, 2015
ii
CONCORDIA UNIVERSITY
School of Graduate Studies
This is to certify that the thesis prepared
By: Jose Luis Garcia Escorcia
Entitled: “Trans-Tibial Amputation as a Model to Evaluate the Role of
Cutaneous Sensation, Proprioception and Muscular Strength on
Balance Performance”
and submitted in partial fulfillment of the requirements for the degree of
Master of Science (Exercise Science)
complies with the regulations of the University and meets the accepted standards
with respect to originality and quality.
Signed by the final Examining Committee:
Veronique Pepin Chair
Cyril Duclos Examiner
Alain Leroux Examiner
Nancy St-Onge Supervisor
Approved by _______________________________________________________
Chair of Department or Graduate Program Director
___________ 201_ ____________________________________
Dean of Faculty
iii
Abstract
Each year, the United States reports around 185,000 limb amputations (Owings & Kozak, 1998).
By the year 2050, amputation’s prevalence is expected to double 2005’ prevalence, affecting
close to 3.6 million of individuals (Ziegler-Graham et al., 2008).
The purpose of this research project was to investigate the role of cutaneous sensation,
proprioception and muscular strength on balance performance in unilateral traumatic trans-tibial
amputees (TTA) under two different conditions, quiet stance and squatting. We proposed that
cutaneous sensation, proprioception and strength are reduced in the non-amputated side of TTA.
In addition, the center of pressure velocity (COPv), the root-mean-square displacement (RMSd)
and the root-mean-square velocity (RMSv) were expected to increase on the non-amputated side.
The last hypothesis was that the decrease of balance performance in traumatic TTA is due at
least in part to reduced cutaneous information, proprioception and strength.
Seven traumatic TTA (6 M/1F, age: M = 36.0, SD = 12.8 years old) and seven able-bodied
controls (6M/1F, age: M = 39.9, SD = 8.1 years old), matched for sex, age, and level of physical
activity, volunteered to participate in this project. Balance assessment was conducted through the
analysis of center of pressure (COP). The evaluation was performed on the non-amputated limb
of traumatic TTA and a randomly selected limb in able-bodied controls during single-legged
stance. The test included three random conditions: 1-standing still with eyes open (EO), 2-
standing still with eyes closed (EC), and 3- squatting with EO. Three additional measurements
on the same limb as balance included: touch pressure sensation (TPS), proprioception, and
muscular strength.
iv
The study revealed significant reduction of COPv and RMSv for the medial-lateral (ML)
direction in amputees as compared to controls. Muscular strength also evidenced significant
differences for the knee and the ankle joints with lower peak-torque-to-body-weight in knee
flexors (FLX) and ankle dorsal-flexor (D-FLX) muscles compared to knee extensors (EXT) and
ankle plantar-flexor (P-FLX) muscles respectively. Significant correlations were observed
between COP variables and muscular strength, in particular to ankle strength.
From our study we can conclude that balance is altered in amputees, with lower values in COPv
and RMSv on the sound limb of amputated individuals as compared to able-bodied controls. This
decrease in COP variables may represent better balance in amputees that could be explained, at
least in part, by amputees relying more on their sound limb on a day-to-day basis during
ambulation and standing. However, lower values of COP variables do not necessarily indicate
better balance performance as a decrease of COP variables may be related to a reduced ability to
control balance.
v
Acknowledgements
First, I want to express sincere thanks to my supervisor Dr. Nancy St-Onge, for enlightening and
guiding me with her knowledge and expertise in all the aspects concerning my work. I appreciate
her support over these years of constant work. She has had the patience to guide, direct, edit and
review my work countless times. She provided me with the necessary and, valued feedback to
learn and progress through this process. She was the person who allowed me to contact the
Constance-Lethbridge Rehabilitation Centre, the Gingras-Lindsay Rehabilitation Centre and
supplied the lab, equipment and facilities that made possible this research.
I would like to thank the financial support from the Natural Sciences and Engineering Research
Council of Canada (NSERC) through the Canada Graduate Scholarship-Master’s (CGS-M) and
thank the Department of Exercise Science for granting me the Graduate Scholarship - Faculty of
Arts and Science, Concordia University.
I wish to thank Ioannis Makris who helped me to set-up the experiments and conduct the pilot
tests for my project. My gratitude also to undergraduate students in the Department of Exercise
Science, Amir Farzaie, Laura Iannella and Kyle L’Esperance for helping me to collect the data
for my project.
I would also like to thank the other members of my supervisory committee, Dr. Cyril Duclos and
Dr. Alain Leroux for providing interesting comments on the methodology of this project. Thank
to Dr. Geofrey Dover for his valuable guide and help with the statistical software and special
thanks to Ron Rehel and Dave Jones, sometimes I just need someone else to talk about life.
vi
I would like to thank Dan Aponte, Mike DeSousa, Amir Farzaie and Alberto Florez, for taking
time to proofread the document and make comments and corrections; I appreciate and value their
time and efforts.
Finally but not the last, I want to thank God for his infinite love and blessings. I would like to
express my enormous love and gratitude to my wife, to my kids, and my parents, in particular to
my mother in heaven. All of them gave me the strength to keep working and trusted in my
abilities even as these were unknown to me. From the very beginning they were my support. To
my parents and my sister, they provided the means for my education, but overall to my parents
who taught me through “love and control”. They taught me what is precious: the love and
support from your family and relatives. I am blessed for having them by my side, my wife,
Sandra, and of course Maria Paula and Daniel Alejandro. They provide me joy, happiness and
the strength to continue, even during my weakest times.
This achievement was possible because all of you were there bringing your support, even if we
cannot see them anymore.
vii
Table of Content
Abstract ....................................................................................................................... iii
List of Figures ............................................................................................................. xi
List of Tables ............................................................................................................. xiii
Abbreviations ............................................................................................................ xiv
Introduction .................................................................................................................. 1
Chapter 1 – Review of Literature. ................................................................................ 3
1.1 Epidemiology of Amputation. ........................................................................... 3
1.1.1 Non-Traumatic Amputations. .................................................................... 4
1.1.2 Trauma-Related Amputations. ................................................................... 4
1.2 Sensation in Amputees. ..................................................................................... 5
1.2.1 Proprioception. ........................................................................................... 6
1.2.1.1 Amputated Limb Vs Non-Amputated Side. ....................................... 6
1.2.1.2 Amputees Vs Able-Bodied Controls.................................................. 7
1.2.2 Cutaneous Sensation. ................................................................................. 8
1.2.2.1 Amputated Limb Vs Non-Amputated Side. ....................................... 9
1.2.2.2 Non-Amputated Side Vs Able-Bodied Controls. ............................. 10
1.3 Muscular Changes in Amputees. ..................................................................... 11
1.3.1 Muscle Atrophy. ...................................................................................... 11
viii
1.3.2 Muscle Strength. ...................................................................................... 11
1.3.2.1 Amputated Limb vs. Non-Amputated Limb. ................................... 13
1.3.2.2 Non-Amputated Limb vs. Able-bodied Controls. ............................ 16
1.4 Balance Control. .............................................................................................. 17
1.4.1 Afferent Information Input. ..................................................................... 18
1.4.2 Center of Pressure. ................................................................................... 20
1.4.2.1 Definitions. ....................................................................................... 20
1.4.2.2 Center of Pressure Measurement. .................................................... 22
1.4.3 Balance in Amputees. .............................................................................. 23
1.4.3.1 Two Limb Stance: Amputees vs. Able-bodied Controls. ................ 24
Static Balance. .............................................................................................. 24
Dynamic Balance. ........................................................................................ 26
Influence of Vision on Balance. ................................................................... 27
1.4.3.2 Two Limb Stance: Amputated vs. Non-Amputated Side. ............... 28
1.4.3.3 Single Limb Stance: Amputees vs. Able-bodied Controls. ............. 29
Chapter 2 – Research Design and Methods ............................................................... 31
2.1 Rationale, Objectives, and Hypotheses. .......................................................... 31
2.1.1 Rationale. ................................................................................................. 31
2.1.2 Objectives and Hypotheses. ..................................................................... 32
Chapter 3 – Research Design and Methods. .............................................................. 33
ix
3.1 Participants. ..................................................................................................... 33
3.2 Balance Assessment. ....................................................................................... 34
3.3 Questionnaires. ................................................................................................ 35
3.3.1 Physical Activity Assessment. ................................................................. 36
3.3.2 Muscular Fatigue. .................................................................................... 37
3.4 Equipment and Measurements. ....................................................................... 38
3.4.1 Balance: Center of Pressure. .................................................................... 39
3.4.2 Cutaneous Sensation: Touch Pressure. .................................................... 39
3.4.3 Proprioception: Joint Threshold Assisted Detection Motion................... 41
3.4.4 Muscular Strength: Peak Torque to Body Weight. .................................. 44
3.5 Procedures. ...................................................................................................... 46
3.6 Data Analysis................................................................................................... 47
3.7 Statistics. .......................................................................................................... 50
Chapter 4 – Results. ................................................................................................... 53
4.1 Level of Physical Activity. .............................................................................. 53
4.2 Level of Muscular Fatigue............................................................................... 53
4.3 Balance. ........................................................................................................... 54
4.3.1 AP and ML Directions. ............................................................................ 54
4.3.2 Standing and Squatting. ........................................................................... 55
4.4 Cutaneous Sensation. ....................................................................................... 58
x
4.5 Proprioception. ................................................................................................ 58
4.6 Muscular Strength. .......................................................................................... 60
4.7 Correlations. .................................................................................................... 62
Chapter 5 – Discussion. .............................................................................................. 63
5.1 Balance. ........................................................................................................... 64
5.2 Cutaneous Sensation. ....................................................................................... 66
5.3 Proprioception. ................................................................................................ 67
5.4 Muscular Strength. .......................................................................................... 69
5.5 Correlations. .................................................................................................... 70
Chapter 6. Limitations. ............................................................................................... 72
Chapter 7 – Conclusions. ........................................................................................... 74
References .................................................................................................................. 75
Appendix A Human Activity Profile ......................................................................... 84
Appendix B Tegner Activity Score ............................................................................ 92
Appendix C Modified Borg Scale .............................................................................. 94
Appendix D Pearson Correlation Coefficients ........................................................... 96
Appendix E Correlation Graphs ............................................................................... 100
xi
List of Figures
Figure 1. Organization of postural control system………………………………………… 18
Figure 2. MatScan® system and electro-goniometer………………………...……………. 35
Figure 3. Experimental procedures for balance assessment………………………………. 38
Figure 4. Touch pressure sensation sites…………….…………………………………….. 40
Figure 5. Proprioception machine…………………………………………………………. 42
Figure 6. Muscular strength measurement settings………………………………..………. 45
Figure 7. Knee angle during dynamic balance assessment………………………………... 50
Figure 8. Mean values of muscular fatigue level…………………………………..……... 54
Figure 9. Mean values of the COP velocity……………………………………………….. 57
Figure 10. Mean values of the RMS velocity……………………………………………... 57
Figure 11. Mean values of the RMS displacement……………………….……………….. 58
Figure 12. Median values of TPS sensation thresholds. …………………………………. 59
Figure 13. Mean values of knee angular displacement for proprioception…………….….. 59
Figure 14. Mean values of peak torque to body weight…………………………………… 61
Figure 15. Mean values of the strength ratios …………………………………………….. 61
Figure 16. Correlation graphs for COP velocity and TPS…………………...………….. 101
Figure 17. Correlation graphs for COP velocity and proprioception………..…………... 102
Figure 18. Correlation graphs for COP velocity and knee muscular strength…………... 103
xii
Figure 19. Correlation graphs for COP velocity and ankle muscular strength……...….. 104
Figure 20. Correlation graphs for COP velocity and muscular strength ratios………….. 105
Figure 21. Correlation graphs for RMS displacement and TPS……..…………………... 106
Figure 22. Correlation graphs for RMS displacement and proprioception………….…... 107
Figure 23. Correlation graphs for RMS displacement and knee muscular strength…...... 108
Figure 24. Correlation graphs for RMS displacement and ankle muscular strength….... 109
Figure 25. Correlation graphs for RMS displacement and muscular strength ratios….... 110
Figure 26. Correlation graphs for RMS velocity and TPS………………….…………... 111
Figure 27. Correlation graphs for RMS velocity and proprioception…….……………... 112
Figure 28. Correlation graphs for RMS velocity and knee muscular strength…………... 113
Figure 29. Correlation graphs for RMS velocity and ankle muscular strength……......... 114
Figure 30. Correlation graphs for RMS velocity and muscular strength ratios……..…... 115
xiii
List of Tables
Table 1. Definitions of the most common measurements used to analyse COP……….… 23
Table 2. Coefficients with significant correlations between COP and other variables….… 62
Table 3. Pearson correlations for COP velocity………………………..……………….… 97
Table 4. Pearson correlations for RMS displacement……………………….……….…… 98
Table 5. Pearson correlations for RMS velocity……………………….…………….…… 99
xiv
Abbreviations
AAS: Adjusted activity score
ABS: Area of the base of support
AKA: Above-knee amputee
ANOVA: Analysis of variance
AP: Anterior-posterior
BKA: Below-knee amputee
CNS: Central nervous system
COG: Center of gravity
COM: Center of mass
COP: Center of pressure
COPv: Center of pressure velocity
CSA: Cross-sectional area
D-FLX: Dorsal-flexor
EC: Eyes closed
EO: Eyes open
EXT: Extensors
FLX: Flexors
HAP: Human activity profile
xv
LLA: Lower limb amputation
MAS: Maximum activity score
ML: Medial-lateral
P-FLX: Plantar-flexor
PT-BW: Peak torque to body weight
RJP: Reproduction of joint position
RMS: Root-mean-square
RMSd: Root-mean-square displacement
RMSv: Root-mean-square velocity
TADM: Threshold assisted detection of motion
TDPM: Threshold detection of passive motion
TPS: Touch pressure sensation
TTA: Trans-tibial amputee
Introduction
Amputation is a surgical procedure, which, in the past 15 years, has risen due to diseases
such as diabetes and peripheral vascular disease (Gregg et al., 2014; Malyar et al., 2013),
and also due to traumatic injuries (Fergason et al., 2010). Commonly, the motor and
somatosensory system reorganizes, and the changes in the representation of the mental
corporal schema seem to be related to the changes imposed by the limb loss (Chen et al.,
2002; Chen et al., 1998; Geurts et al., 1991; Karl et al., 2001; Kavounoudias et al., 2005).
The loss of large portions of tissue from a body segment leads to changes of different
body systems (Chen et al., 2002; Chen et al., 1998). The missing information from the
amputated segment is also associated with the loss or reduction of sensation
(Kavounoudias et al., 2005; Kosasih & Silver-Thorn, 1998), altered proprioceptive
information (Eakin et al., 1992; Kavounoudias et al., 2005), and changes in muscular
strength (Isakov et al., 1996b; Moirenfeld et al., 2000; Nadollek et al., 2002; Pedrinelli et
al., 2002; Renstrom et al., 1983a) as well as changes in balance performance (Dornan et
al., 1978; Duclos et al., 2009; Duclos et al., 2007; Fernie & Holliday, 1978; Gauthier-
Gagnon et al., 1986; Geurts et al., 1991; Hermodsson et al., 1994; Isakov et al., 1992).
Despite the fact that numerous studies have evaluated the effect of amputation on
multiple variables, there is no clear explanation of how these variables influence balance
control.
The following literature review contains some epidemiological data related to
amputation. We also present different aspects related to: TPS, proprioception and
2
muscular strength. These variables are all commonly accepted measures studied in
amputated individuals. We discuss the changes affecting not only the amputated side, but
also the non-amputated side. We also considered other subjects like balance response
under static and dynamic conditions, and the influence of vision on balance performance.
3
Chapter 1 – Review of Literature.
1.1 Epidemiology of Amputation.
Each year, the United States reports around 185,000 limb amputations (Owings & Kozak,
1998). The National Health Interview Survey in 1996 estimated that 1.2 to 1.6 million
persons in the US lived with a limb amputation (Adams et al., 1999). According to
Ziegler-Graham et al. (2008) the forthcoming prevalence of limb loss for the year 2050 in
the US will be more than double the estimated prevalence for 2005 (about 3.6 million in
2050). Statistical data from 2005 indicated that 54% were amputations related to
dysvascular disease among older adults and 45% of the amputation procedures were
related to trauma. The remaining 1% percent corresponded to cancer-related amputations.
Independent of the origin, amputation imposes a significant health, social and economic
burden (Clarke et al., 2003; King et al., 1998; Moulik et al., 2003). In developed
countries, non-traumatic etiology is considered the main cause of lower limb amputations
(LLA) (Manchester et al., 1989; Ziegler-Graham et al., 2008) compared to developing
countries, which report trauma as the primary cause of LLA (Collin & Collin, 1995)
affecting both combatants (Fernie & Holliday, 1978; Islinger et al., 2000), and civilians
(Meade & Mirocha, 2000). Moreover, trauma related amputation affects a significant
number of younger individuals generating a great impact on life among young,
previously healthy individuals (Laupland et al., 2005).
4
1.1.1 Non-Traumatic Amputations.
Non-traumatic lower-extremity amputation is a condition that increases with aging,
affecting elderly people (Dillingham et al., 2002; Ziegler-Graham et al., 2008). It is
considered the primary cause of morbidity and mortality among individuals with diabetes
and dysvascular disease diagnosis (Dillingham et al., 2002; Ebskov et al., 1994; Ziegler-
Graham et al., 2008). From all dysvascular amputation procedures, around 60% were
major limb amputations. According to the authors, among amputees from all etiologies,
65% of the procedures were performed on the lower extremity (Ziegler-Graham et al.,
2008).
Major non-traumatic limb amputations have a high correlation with diabetes. Ziegler-
Graham et al. (2008) estimated that two-thirds from a total of 54% of dysvascular
amputees were linked to a diabetes diagnosis in the US. In the future, an increase in
major limb amputations is expected considering the expected increase of diabetes
prevalence from 2.8% in 2000 to 4.4% in 2030 (Ebskov et al., 1994; Wild et al., 2004).
1.1.2 Trauma-Related Amputations.
Trauma is considered the second leading cause of amputations in developed countries
(Dillingham et al., 2002; Owings & Kozak, 1998). According to some studies, which
included amputees from different etiologies trauma-related amputation affect more the
upper limbs (Dillingham et al., 2002; Ziegler-Graham et al., 2008). However, the study
by Barmparas et al. (2010) who analyzed only traumatic amputees, reported that 59% of
single extremity amputations affected the lower extremity, most of them below knee
level. The other 41% affected the upper extremity. They also reported a higher frequency
5
of LLA in pedestrians and motorcyclists compared to motor vehicle occupants whom
displayed more upper extremity amputations (Barmparas et al., 2010). Traumatic
amputations related to age and sex report controversial results. According to Dillingham
et al. (2002), amputation increased with age for all, traumatic and non-traumatic cases
and was independent of sex and race. Laupland et al. (2005) also reported a higher
incidence of amputation in the elderly, and Ziegler-Graham et al. (2008)indicated that
men had five times higher risk of trauma-related amputations compared to women. Note
that Ebskov et al. (1994) described two major peaks for male trauma-related amputation:
one at the ages 20 to 29 and the second from 70 to 79 years. Female traumatic amputees
showed a single peak only for the ages 70 to 79.
1.2 Sensation in Amputees.
Different studies reported changes in sensorimotor representation in traumatic and non-
traumatic amputees (Braune & Schady, 1993; Chen et al., 1998; Geurts et al., 1992;
Simoes et al., 2012). Changes in the sensorimotor representation may also lead to a
cortical and neural structural reorganization of the non-amputated side (Simoes et al.,
2012). Those changes could explain in part why the non-amputated side is affected in
both vascular and traumatic amputees.
The loss of anatomical structures implies the deprivation or altered sensation information
from musculoskeletal, articular and cutaneous tissues (Geurts et al., 1992). The
amputation could generate significant changes on afferent information related to
proprioception and cutaneous sensation (Kavounoudias et al., 2005).
6
1.2.1 Proprioception.
Proprioception is defined as “the sensory information from the muscles, tendons, or joints
about limb position and movement” (Gaither, 2008), or the sensory awareness of body
position essential for motor control (Lackie, 2010). The ability is derived from the neural
afferent information related to joint motion, spatial localization and force generation
sensations processed by the central nervous system (CNS) (Lephart & Fu, 2000). The
most frequent methods used to assess the perception of joint movements and positions are
the threshold detection of passive motion (TDPM) and the reproduction of joint position
(RJP). The TDPM measurement is based on the perception of joint motion. The joint to
be evaluated is passively displaced at a very low angular speed, and individuals indicate
the perception of the joint displacement using a control device. The test measures the
difference between the starting angle and the angle where motion is perceived. The RJP
procedure also involves the passive movement of the joint from the starting point to a
pre-set target angle. The joint is held at this target angle for a few seconds and then it is
repositioned to the starting angle. After that, the participants are then asked to bring the
joint to the target angle. The evaluation of this test involves measuring the difference
between the pre-set target angle and the angle reached by the voluntary displacement.
1.2.1.1 Amputated Limb Vs Non-Amputated Side.
Eakin et al. (1992) and Liao & Skinner (1995) studied the TDPM in unilateral lower limb
amputees. Liao & Skinner (1995) evaluated the TDPM in vascular and traumatic below-
knee amputees (BKA) at a speed displacement of 0.4°/second while the participants were
seated. Eakin et al. (1992) evaluated traumatic and cancer related above-knee amputees
7
(AKA) (Nakagawa et al., 1993) at the speed of 0.5°/second while the participant was
standing. Both Eakins’s and Liao’s studies reported higher TDPM values in the
amputated limb compared to the non-amputated limb (sound limb of amputees).
Kavounoudias et al. (2005) also evaluated the TDPM under non-weight bearing
conditions in traumatic and non-traumatic (vascular) BKA amputees. The participants
were seated while the joint was displaced at the speed of 0.7°/second. However, in their
results Kavounoudias et al. (2005) reported no difference in TDPM between the
amputated and the non-amputated limb. In their studies, Eakin et al. (1992) and Liao &
Skinner (1995) also included the assessment of the RJP. Both studies displayed no
difference between the amputated and the non-amputated side of unilateral lower limb
amputees.
1.2.1.2 Amputees Vs Able-Bodied Controls.
Liao & Skinner (1995) and Kavounoudias et al. (2005) not only compared the amputated
limb to the non-amputated limb side. They also included able-bodied controls to make the
comparisons. They reported that the TDPM in the non-amputated side of amputees was
higher when compared to able-bodied controls. Moreover, Kavounoudias et al. (2005)
separately compared vascular and traumatic amputees to able-bodied controls. When the
sound limb of amputees was compared to able-bodied controls, both traumatic and
vascular amputees exhibited significant differences in TDPM at knee but not at the ankle
joint level. Knee joint in amputees showed higher TDPM values compared to controls.
Liao’s study compared RJP between the amputated limb and able-bodied controls,
reporting no difference among these two groups.
8
Despite the absence of differences in RJP, significant differences are evidenced in TDPM
in both limbs of amputees. These results support the existence and involvement of
different mechanisms in the proprioceptive regulation of joint motor control
(Kavounoudias et al., 2005). Based on the results, Kavounoudias, et al. (2005) suggested
that amputees compensate the absence of proprioceptive information from missing
anatomical structures. They could gather additional information from other sources or
using other means such as the displacement of adjacent joints, changes on superficial and
deep pressure sensors and modifications on soft tissues receptors. Liao & Skinner (1995)
also suggested that muscle spindles could be more susceptible to perceive small changes
of joint angles and muscle length than able to reproduce the angle of joint repositioning.
1.2.2 Cutaneous Sensation.
Cutaneous sensation is defined as the perception originating from receptors of the skin.
Touch perception includes “several partially independent senses” such as thermal
sensation (warmth – cold), cutaneous touch-pressure (superficial – deep), vibration, pain,
itch, and “movement across the skin” (Kalat, 2013). Different tests used to evaluate
cutaneous sensation are usually applied on pressure-tolerant and pressure-sensitive areas
and may be influenced by the loss of tissues in amputees (Murdoch, 1969). In amputees,
sensory impairment could be influenced by factors like age and time since amputation
(Kosasih & Silver-Thorn, 1998).
9
1.2.2.1 Amputated Limb Vs Non-Amputated Side.
The procedures used to assess sensation in amputees varied between different studies
(Kavounoudias et al., 2005; Kosasih & Silver-Thorn, 1998). In these studies, amputees
evidenced an altered perception of the cutaneous sensory information. Kosasih & Silver-
Thorn (1998) compared sensation between the amputated and the non-amputated side of
traumatic and non-traumatic amputees. They evaluated symmetry and asymmetry
perception of light touch, deep pressure, vibration, and pinprick sensation in amputees.
To standardize the assessment perception of these parameters they included cotton swabs,
a tuning fork and, the sharp and dull ends of a safety pin. Only deep pressure did not
include an instrument, but they used the examiners’ thumb to evaluate the sensation.
"Normal" sensation was established as the ability to perceive or not, the applied stimulus.
Results were reported as the comparison in sensation perceived on the amputated side
compared to the non-amputated side (sensation amputated/sensation non-amputated). A
“normal/normal” condition indicated a normal sensation on both sides. Three more
combinations were also presented in the study (impaired/normal, normal/impaired and
impaired/impaired). Out of 16 participants, 7 displayed altered sensation in the non-
amputated side and were excluded from additional analysis. Among the participants who
evidenced non-altered sensation in the non-amputated side (8 traumatic and 1 cancer
related amputee) the most affected sensation on the amputated side was pin prick (67%
overall participants). Altered pin prick sensation was also related to age and time since
the amputation. Sensory impairment affected 60% of middle aged participants (45 - 59
years) and 100% of participants aged 60 years old or more. All the participants with 10
years or less since the amputation or those with 21 year or more also revealed a sensory
10
impairment of 100% and 75% respectively. Moreover, these participants evidenced an
altered perception of light touch and vibration perception (11% of the participants for
each group). The results did not evidence alterations in deep pressure sensation.
Researchers suggest that the deterioration of the sensory perception on the non-amputated
limb seems to be related to different conditions such as bilateral trauma, diabetic
polyneuropathy, and or prior vascular surgery (Kosasih & Silver-Thorn, 1998).
Kavounoudias et al. (2005) reported different results when comparing the amputated and
the non-amputated extremities depending on the origin of the amputation. They indicated
that traumatic, but not vascular amputees exhibited significant differences in TPS
between tibial sites. Traumatic amputees displayed higher TPS levels on the amputated
side compared to the non-amputated side.
1.2.2.2 Non-Amputated Side Vs Able-Bodied Controls.
The study by Kavounoudias, et al. (2005) also compared the TPS between the sound limb
of amputated individuals and able-bodied controls, reporting that cutaneous sensation
impairment also affected the non-amputated side. Due to significant differences in age
and time since the amputation between vascular and traumatic amputees, they were
analysed independently. When comparing only the non-amputated side of traumatic
amputees to able-bodied controls, the TPS demonstrated higher values. This difference
was significant only at the plantar site, not at the tibial site. The results for vascular
amputees did not display differences in TPS when they were compared to able-bodied
controls. However, vascular amputees evidenced significant differences for the testing
site, with lower TPS thresholds at the tibial site compared to plantar site.
11
1.3 Muscular Changes in Amputees.
Muscle tissue has been considered as an effector "organ" responsible for generating the
force necessary to develop joint movement and body displacement. Amputation,
regardless of the origin causes the loss of different tissues mainly musculoskeletal tissue
involved in the generation of muscular force.
1.3.1 Muscle Atrophy.
Different methods have been used to describe muscular changes in amputees in order to
explain the reduction of muscular strength (Isakov et al., 1996a; Renstrom et al., 1983a;
Schmalz et al., 2001). These methods ranged from low to high technology devices
including: measuring tape (Isakov et al., 1996a; Renstrom et al., 1983a), biopsy analysis,
computed tomography, magnetic resonance image measurements (Renstrom et al.,
1983a) and ultrasound techniques (Schmalz et al., 2001).
Renstrom et al.(1983a) used BKA due to vascular and non-vascular origin to describe
muscle atrophy associated with an amputation. The authors performed muscular biopsies
of the vastus lateralis of the amputated and the sound limb sides and compared the
muscles’ fiber distribution. They also studied the effect of amputation on the cross-
sectional area (CSA) of the thigh using computed tomography and on the whole thigh
perimeter using a measuring tape. The authors conducted the evaluation of the CSA and
the thigh perimeter assessment at the same level where they performed the muscular
biopsies.
12
The biopsies result showed no differences in the fiber type distribution between the
amputated and the sound limb. However, there was a trend to a reduction in fiber type I
(from 38% to 33% approximately) and a trend of increments in fiber type II (from 62% to
67% approximately). Conversely, the analysis of muscle fiber II subtypes showed
significant differences in the percentage of fiber distribution. The amputated side
evidenced with a smaller fraction of type IIA fibers and a bigger fraction of type IIB and
IIC fibers. When they evaluated the CSA, the whole thigh evidenced lower values in the
amputated side, representing 86% of the CSA of the sound limb side. The compromise of
quadriceps muscles was higher than hamstring muscles evidencing a higher reduction of
CSA; quadriceps muscles exhibited a 66% and hamstring muscles 80% of the CSA of the
non-amputated leg muscles respectively.
Different studies indicated that the measuring tape might not detect large differences in
muscles’ CSA (Lexell et al., 1983; Young et al., 1980). However, the results reported by
Renstrom et al. (1983a) revealed that the difference between the level of atrophy
measured by computed tomography and the level of atrophy using the measuring tape
was less than 2%. Both measurements suggested a reduction in muscular CSA in the
amputated side compared to the non-amputated side.
Another method used to evaluate muscular changes between the amputated, and the non-
amputated side was ultrasonography showing significant reductions in muscular
thickness and CSA in the amputated side (Schmalz et al., 2001). However, the CSA
indicated a higher compromise with a mean reduction of 21% compared to the muscle
thickness that evidenced a mean reduction of 13%. This compromise affected specific
13
muscular groups, with significant changes in rectus femoris, vasti and sartorius but no
difference in muscle thickness and CSA for the gracilis, semitendinosus and biceps
femoris muscles.
1.3.2 Muscle Strength.
By contracting the muscle fibres, it is possible to develop the force necessary to produce
the movement (acceleration - deceleration) of different body segments. Muscular strength
is influenced by the level of muscle mass (Gopalakrishnan et al., 2010; Hurley, 1995;
Kasper et al., 2002). In amputees, sarcopenia and the associated reduction of muscular
fibre CSA (Renstrom et al., 1983b) could lead a reduction of force generation (Isakov et
al., 1996b; Moirenfeld et al., 2000; Pedrinelli et al., 2002; Renstrom et al., 1983b).
Changes in muscular strength may influence the rehabilitation outcomes and eventually
the adaptation of prosthetic use in amputated individuals (Isakov et al., 1996b).
The measurement of muscle strength can be performed through different methods
including dynamometers. Dynamometers are considered the most reliable method to
evaluate the force (Bandy & McLaughlin, 1993; de Carvalho Froufe Andrade et al., 2013;
Holmback et al., 1999; Orri & Darden, 2008).
1.3.2.1 Amputated Limb vs. Non-Amputated Limb.
Various studies compare muscular strength levels between the amputated and the non-
amputated extremity in amputees to evaluate the level of strength compromise. These
studies evaluated amputees from traumatic and non-traumatic etiologies (Isakov et al.,
1996b; Isakov et al., 1996a; Pedrinelli et al., 2002; Renstrom et al., 1983b). One single
14
study evaluated only traumatic amputees (Moirenfeld et al., 2000). Independent of the
origin and level of amputation, most of the studies reported significant reduction of thigh
muscles strength in the amputated side including peak torque (Isakov et al., 1996b;
Moirenfeld et al., 2000), isometric force (Isakov et al., 1996b), maximum bending
moment, total work and total power (Pedrinelli et al., 2002).
The following studies evaluated BKA, performing the assessments at different isokinetic
speeds: Renstrom et al. (1983b) evaluated strength at 30°, 60° and 120°/second,
Pedrinelli et al. (2002) at 60°/sec and 180°/second, Isakov et al. (1996a) at 60°/sec and
Moirenfeld et al. (2000) at 120°/second. All the studies, except Isakov et al. (1996b;
1996a) evaluated strength (peak torque) during consecutive concentric knee FLX and
knee EXT, but also included the eccentric isokinetic strength measurement of the same
muscles. Isakov et al. (1996b; 1996a) evaluated knee FLX and EXT muscles using
eccentric isokinetic strength measurement. Isakov et al. (1996b; 1996a) and Renstrom et
al. (1983b) also assessed isometric strength.
In general when the amputated side was compared to the non- amputated side, different
studies revealed significant reductions of concentric and eccentric knee FLX and EXT
strength. Other significant differences are related to the assessed muscular group. Knee
EXT muscles evidenced higher reduction of isometric (Renstrom et al., 1983b) and
isokinetic muscular strength compared to knee FLX muscles (Moirenfeld et al., 2000;
Renstrom et al., 1983b). However, Pedrinelli et al. (2002) suggested the opposite; they
indicated that peak bending moment reductions were more evident for the knee FLX than
for knee EXT muscles when comparing the amputated side compared to the non-
15
amputated side. Despite reporting significant differences between the amputated side and
the non-amputated side, Isakov et al. (1996a) described no differences between knee FLX
and knee EXT muscles.
Moirenfeld et al. (2000) also evaluated the isokinetic endurance using a fatigue index.
The fatigue index was calculated as the difference in total work from the first ten and the
last ten repetitions, divided by the total work during the first 10 repetitions. The
amputated limb evidenced lower levels of the fatigue index than the sound limb. This
deficit was statistically significant for EXT muscles but not for FLX muscles.
In another study by Nadollek et al. (2002) they evaluated a different muscular group and
also used a different method of assessment. Using a manual dynamometer, they evaluated
the hip abductor muscles of each limb in traumatic and vascular BKA. The assessment
included the peak force of maximum isometric abduction of the hip. However, Nadollek
et al. (2002) did not report significant differences in strength measurements between the
amputated and the non-amputated limb.
The length of the amputated residual extremity was an additional factor that yielded a
significant role on strength of BKA. In a supplementary report by Isakov et al. (1996b),
concentric, eccentric and isometric strength for the knee FLX and EXT muscles
displayed lower values in those amputees with shorter remnant limb (less than 15 cm)
than those with the butt end length higher than 15 cm. However, Pedrinelli et al. (2002)
did not demonstrate a relationship between force reduction and those amputated
individuals with shorter residual limb length.
16
Renstrom et al. (1983b) evaluated the effect of muscle atrophy on strength, reporting
significant correlations with the CSA for the amputated limb. They reported a significant
correlation between CSA and muscular strength for knee FLX and EXT, when the
participants were using the prosthesis and only for knee EXT during isometric
contractions. No correlations were revealed between CSA and muscular strength for the
non-amputated side. The authors indicated that the large reduction in muscular strength
compared to the slow progress in muscular atrophy suggested the existence of concurrent
factors, other than muscular atrophy (e.g.: reflex inhibition). These factors could explain
the reduction of muscular strength on the non-amputated side.
1.3.2.2 Non-Amputated Limb vs. Able-bodied Controls.
When they evaluated the strength levels of amputees Pedrinelli et al. (2002) not only
compared the amputated limb to the sound limb, but they also compared the sound limb
of amputated individuals to limbs of able-bodied controls. Amputees showed significant
reductions for all the measures at the different speeds assessed in maximum bending
moment, total work and maximum power. With these results, the authors concluded that
the use of the non-amputated limb as reference to evaluate the muscular strength of the
amputated side in amputees is an inadequate comparison. To our knowledge, no other
study compared the level of muscular strength of the amputated limb in TTA to the level
of muscular strength in able-bodied controls.
17
1.4 Balance Control.
Balance is an expression used to describe all the postural changes in order to maintain the
projection of the body’s center of mass (COM) within the limit area of the base of
support (ABS) (Mooren, 2012). Balance control is a multi-faceted motor skill influenced
by the coordinated activation of extremities and trunk muscles (Horak et al., 1997). The
balance-control system also maintains a particular body orientation and stability under
static and dynamic conditions (Deliagina et al., 2012).
The CNS plays a crucial role in balance control by integrating the sensory input
information coming from different structures and tissues (Figure 1). Experimental animal
models reported that in addition to the motor cortex, basic mechanisms for postural
balance control are located at lower levels of CNS, within the brainstem and cerebellum
(Deliagina et al., 2007; Deliagina et al., 2012). After processing this information, the
CNS generates a coordinated series of motor responses, adjusting the orientation and
position of different body segments (Massion, 1998).
The CNS system is capable of controlling posture using different strategies including:
anticipatory responses, compensatory responses, or combination of both (Maki &
McIlroy, 1997). The anticipatory strategy, also called “predictive” strategy, seems to
imply the voluntary activation of various muscles as an expected response to potential
changes in posture. The second is the compensatory or “reactive” strategy. This may
include the muscular response and the associated postural adjustments that follow an
unpredicted perturbation of balance (Maki & McIlroy, 1997). Thus, postural control
should not be considered only as an automatic response, but also as a motor skill that
could be learnt or trained (Horak et al., 1997).
18
Figure 1. Organization of the postural control system. The diagram summarizes the
principal structures involved in postural control. The CNS integrates and processes
the afferent information to generate an efferent response (muscular activation).
Modified from Massion, 1994.
1.4.1 Afferent Information Input.
Most studies evaluating balance control assess the role of vision, vestibular, and
proprioceptive information. Different sensors register the gravity force and other forces,
which typically occur during motion. The signals are transmitted and, integrated by the
CNS and then compensated by the coordinated activation of different muscular groups.
These internally processed signals then lead to anticipatory postural responses to
maintain balance. These signals in their large majority are produced by the action of the
voluntary muscles activity (Bloem et al., 2000; Massion, 1994; Mergner & Rosemeier,
1998). These anticipatory adjustments play a significant role in the feed-forward and
feed-back response that helps to maintain balance (Dietz et al., 1993).
19
The somatosensory input from muscles, joints and cutaneous receptors represents one of
the primary sources of information for balance control. Proprioceptive sensors which
provide information related to muscle length (muscle spindle fibres), muscular tension
(Golgi tendon organ) and the articular angle position (Ruffini’s ending receptors), allow
the spatial location of different body segments (Gandevia & Burke, 1992; Mohapatra et
al., 2012). Some studies considered that proprioceptive information from muscles which
control the ankle joint play a significant role in body position changes (Barbieri et al.,
2008; Nakagawa et al., 1993).
The influence of visual information on balance has been evaluated mainly from two
different perspectives. The first one is related to the effect of the visual fields and the
visual object-motion perception on postural sway (Dijkstra et al., 1994; Previc et al.,
1993). According to Dijkstra et al. (1994) the visual information from peripheral and
central visual fields equally affects postural sway. In addition they suggest the existence
of a dynamic coupling between the moving visual environment and postural sway and the
slight retinal displacement that occurs under moving visual environment does not explain
the changes in postural sway. The second perspective used is the evaluation of COM
modifications associated to changes of the ground-reaction forces when switching from
EO to EC condition. By measuring the center of gravity (COG) displacement or the COP
displacement, calculated from ground reaction forces (Deliagina et al., 2007), various
studies reported that COP displacement is more evident under EC condition (Baltich et
al., 2014; Chen et al., 2014; Kanekar et al., 2014; Tsai et al., 2008).
When the visual information is reduced or absent, the vestibular system plays a
significant role in the perception of changes of body inertia specially the head angular
20
acceleration (Mergner & Rosemeier, 1998). The semicircular canal systems provide more
information related to angular acceleration while the otolith systems provide more
information related to linear acceleration. For balance control, the information from these
two subsystems has to be combined. Some authors considered that the information from
these signals is not ideal due to the delay generated by the synthesis process (Mergner &
Rosemeier, 1998). Some others considered that vestibular information might not
represent a major source of information during early postural change response to balance
perturbations. The vestibular system has been shown to induce the activation of the hip
strategy (Winter, 1995). This strategy involves the muscular activation sequence from the
proximal-to-distal body segments and also the activation of the trunk muscles (Allum et
al., 1993; Horak et al., 1994; Mergner & Rosemeier, 1998).
1.4.2 Center of Pressure.
1.4.2.1 Definitions.
It is important to define first the COM and COG, which are completely different from the
COP (Palmieri et al., 2002).
The COM could be defined as the point where the total mass of the body is concentrated,
representing the sum of the “weighted average” of all the different body segments COM
locations (Newman, 2008; Winter, 2009). This center is considered the point of action of
all external forces and it is used to analyze and understand body “translational motion”
(Newman, 2008). The COG is defined as the vertical projection of the COM from the
floor (Palmieri et al., 2002; Winter, 2009). The center can be modified by the position
21
and/or the displacement of different body segments. In addition, it is also the point of
reference for the postural control system to adjust and maintain balance (Winter, 2009).
The COP is a point that represents the mean weighted average from the area of support,
where all the ground reaction forces act. Winter (1995) considered the COP as the vector
position of the vertical ground reaction forces. The position of this vector represents also
the projection of the muscular forces required to maintain balance (Winter, 2009; Winter
et al., 1990). The COP reveals the course followed by the COM. The path followed by
the COM can be correlated to the path followed by the COP yet, as explained before they
are entirely different (Palmieri et al., 2002).
The displacements and adjustments of the COP during quiet standing are due mainly to
the activity of the ankle, hip and trunk muscles leading to body sway. During quiet
stance, the body sways sideways between the lower extremities and, forward and
backward swivelling around the ankle joints. Changes in the COP through body sway
help to control the body COM. When the somatosensory system perceives the anterior
displacement of the body COM, the COP is displaced forward toward the edge of the area
of base support, in front of the COM. The coordinated activation of different muscular
groups, which modify the COP, reduces or stops the displacement of the COM and
reverses its forward translation. The muscular activation also generates the displacement
of the COM backwards and now the COP follows the COM in the opposite direction and
the entire process is repeated now for the posterior direction (Winter, 1995, 2009; Winter
et al., 1990).
22
The main objective of the process described before is to maintain the COM within the
base of support. However, greater displacements of the COM are associated with greater
displacements of the COP. This activity also implies a higher trend to reach a point where
the COM is displaced outside the ABS. Outside this area, it is necessary to adjust the
posture in order to maintain the body balance (Horstmann & Dietz, 1990; Winter, 1995,
2009). During single-legged stance, the COP is located within the area of contact of the
foot. During two-legged stance the COP moves within a zone located between the two
feet and is influenced by the relative distribution of body weight (Winter, 2009; Winter et
al., 1990).
1.4.2.2 Center of Pressure Measurement.
The COP can be measured using a force plate or a pressure mat system. Data from the
force plate measures the force in three dimensions but only the vertical components are
necessary to calculate the COP (Winter, 2009). The pressure sensing systems also
measure the vertical component of the ground reaction force derived from the area in
contact with the feet (Orlin & McPoil, 2000).
COP data is recorded as a successive coordinate points (x and y) system related to time.
Table 1 summarizes the most common measurements used to analyze the COP
performance in able-bodied individuals and also in amputees (Abrahamova & Hlavacka,
2008; Buckley et al., 2002; Isakov et al., 1992; Palmieri et al., 2002).
Conditions like neurological diseases, musculoskeletal disturbances or any modification
of the systems which provide or integrate the information could generate an inappropriate
23
response of body effectors. The loss of tissues in lower-limb amputees and the related
information also affects body posture and may predispose to balance impairment.
1.4.3 Balance in Amputees.
To minimize the displacement of the COM above the base of support, it is necessary the
continuous control by the COP. The upright position is a less stable condition which
requires a greater control of the COM and also demands a higher activity from the centers
of control (Korr, 1975). The study of balance in amputees has included many different
conditions and settings trying to explain how balance is affected in these individuals.
COP VARIABLE DESCRIPTION
Maximum amplitude Maximum absolute displacement of the COP from its
average point.
Minimum amplitude Minimum absolute displacement of the COP from its
average point.
Peak-to-peak amplitude Difference between the maximum and minimum
amplitudes of COP.
Mean amplitude of COP The average value over all data points collected in a
trial.
Total excursion - Displacement Sum of distance between COP successive points.
COP velocity Total displacement traveled by the COP over time.
Root-mean-square amplitude Standard deviation of the COP position.
Root-mean-square velocity Standard deviation of the COP instantaneous velocity.
Spectral analysis Detect what frequencies existed in the data, related to
a particular sensory system.
Time-Frequency analysis Study the frequency characteristics over time,
associated to a specific sensory system
Table 1. Definitions of the most common measurements used to analyse the COP
(Palmieri et al., 2002).
24
1.4.3.1 Two Limb Stance: Amputees vs. Able-bodied Controls.
A considerable number of research studies on balance in amputees performed
assessments during double-legged stance and almost all of them reported increments in
postural sway in amputated individuals when compared to able-bodied controls. Different
parameters were used to measure balance performance including the COP excursion
range and the sum of the squares deviations from the mean COP in the anterior-posterior
(AP) (Shapiro, 2013) and ML direction (Buckley et al., 2002), the mean speed of sway in
AP and ML direction (Dornan et al., 1978; Fernie & Holliday, 1978), and the root mean
square of the COP velocity (Geurts et al., 1991). In this section, we will use the term
"postural sway" as a general term that includes all the variables used in different studies
to evaluate balance.
Static Balance.
In BKA, significant differences have been evidenced for postural sway, with higher
values in amputees as compared to able-bodied controls. Although the test was performed
during bipedal position, these differences were even larger under EC conditions (Dornan
et al., 1978; Fernie & Holliday, 1978; Isakov et al., 1992). When compared to able-
bodied controls, all BKA (traumatic and vascular) displayed significant differences only
for ML directions under EO condition. Significant differences were reported for both AP
and ML direction only under EC condition (Hermodsson et al., 1994). Amputated
individuals and vascular amputees in particular revealed significant increments in the
standard deviation of the COP position (Hermodsson et al., 1994). When compared
separately to able-bodied controls under EO condition, vascular amputees displayed
25
significant differences in ML direction and traumatic amputees only evidenced
significant differences in AP direction.
The standing time in balance was also impaired in BKA amputees. Hermodsson et al.
(1994) evaluated balance in amputees from different etiologies during double-legged
stance compared to able-bodied controls. All the amputated participants and vascular
amputees in particular displayed a significant shorter standing time compared to able-
bodied controls (Hermodsson et al., 1994). Significant reduction in standing time was
also evident in vascular amputees when compared to traumatic amputees. No significant
difference was revealed for standing time between traumatic amputees and able-bodied
controls (Hermodsson et al., 1994).
However, Gauthier-Gagnon et al. (1986) reported different results compared to other
studies. They demonstrated reductions of postural sway in AKA and BKA individuals
from traumatic and non-traumatic origin. They measured and compared the mean surface
of sway of amputees under two different rehabilitation programs and able-bodied
controls. Either under EO or EC, able-bodied controls exhibited a mean surface of sway
of 14 ± 13 cm2 representing almost 2% of the ABS. The initial assessment of both, the
experimental and the conventional rehabilitation groups displayed a reduced sway surface
area of 1.9 ± 1.3 cm2 and 3.3 ± 1.0 cm
2 respectively. Despite an increase of sway surface
area after the rehabilitation program, these values were still significantly reduced in both
groups when compared to able-bodied controls. The change represented less than 0.3% of
the total ABS leading to a less stable condition.
26
In AKA individuals, it was expected that the proximal location of the amputation
imposed a greater demand not only to the remaining structures (stump and sound limb)
but also to the different systems responsible for controlling the posture and balance.
Considering the greater loss of tissue, researchers expected more changes in balance
performance in AKA individuals. However, results seem controversial. In some cases,
AKA demonstrated no differences in balance performance when compared to able-bodied
controls (Dornan et al., 1978; Fernie & Holliday, 1978). In other cases, AKA revealed
significant higher levels of postural sway in AP and ML direction when compared to
able-bodied individuals (Buckley et al., 2002; Geurts et al., 1991). It is drawn the
attention to an interesting result observed when comparing AKA and BKA individuals.
Despite the smaller extremity level of amputation, BKA described higher levels of
postural sway when compared to AKA, or when compared to able-bodied controls
(Dornan et al., 1978; Fergason et al., 2010).
Dynamic Balance.
One study not only evaluated balance under static conditions, they included also dynamic
balance assessment in amputees. Buckley et al. (2002) separately evaluated dynamic
postural sway in traumatic AKA and BKA individuals using a modified single axis
stabilimeter. Results evidenced reduced values for time in balance in amputees when
compared to able-bodied controls. The number of board contacts was reported to be
similar in both groups. The comparisons between amputees and able-bodied individuals
did not indicate differences in the results for any of the tested conditions (platform tilt in
AP and ML directions). However, more board contacts were displayed on the amputated
side compared to the non-amputated side in amputees. The authors also stated that able-
27
bodied individuals did not report significant differences in the number of board contacts
between both sides. They suggested that increments in board contacts on the amputated
side might be used as an additional source of somatosensory information. This
information could improve amputees’ response to balance perturbations. Despite the
trend to increments in mean time spent during board contact (more evident in AP task),
the results indicated no differences when comparing amputees and able-bodied
individuals.
Influence of Vision on Balance.
The influence of visual information is the most common factor involved in balance
performance assessment. Independent of the amputation level or the etiology, visual
information seems to exert an important role in balance performance in amputees
(Dornan et al., 1978; Fernie & Holliday, 1978; Geurts et al., 1991; Isakov et al., 1992). In
general, under EC condition, amputated individuals displayed a less stable condition
when compared to able-bodied controls (Buckley et al., 2002; Dornan et al., 1978; Fernie
& Holliday, 1978; Geurts et al., 1991; Isakov et al., 1992). Despite reporting no changes
in the weight-bearing distribution, Isakov et al. (1992) reported that postural sway was
increased while the participants were blindfolded.
The ratio EO to EC of the mean speed of sway of AKA and BKA evaluated by Fernie &
Holliday (1978) described significant differences when amputees were compared to able-
bodied controls. Both groups of amputees evidenced lower ratio values. This difference
was even greater for AKA, which exhibited the lowest ratio values. The lower ratio EO to
28
EC in amputees may indicate the importance that visual information plays on the control
of balance in those individuals (Fernie & Holliday, 1978).
1.4.3.2 Two Limb Stance: Amputated vs. Non-Amputated Side.
Nadollek et al. (2002) compared the amputated limb to the non-amputated limb during
two-legged stance in non-traumatic BKA. The measurements included the standard
deviation of ML and AP COP excursion and the percentage of weight-bearing
distribution during quiet stance or standing still while distributing evenly the body weight
(even stance). Due to the absence of differences between quiet and even stance, the
authors reported the comparisons using only the quiet stance condition. The authors
stated that the non-amputated side supported significantly more weight compared to the
amputated side during quiet stance. During double-legged stance under EO condition
amputees displayed higher displacements of COP in AP direction under the non-
amputated limb compared to amputated limb. Moreover, under EC condition the non-
amputated limb indicated a trend to larger displacements in AP direction. The analysis of
ML direction did not display differences between extremities or significant differences
related to eyes condition. However, the authors reported a trend of higher values in ML
direction when amputated limb side was compared to the non-amputated side.
Duclos et al. (2009; 2007) described the postural asymmetry in LLA, reporting a shift of
the COP position to the non-amputated side. These studies described the effect of muscle
vibration (trapezius - gluteus medius) (Duclos et al., 2007) and the effect of isometric
neck muscle contraction (Duclos et al., 2009) on standing posture and balance. The
29
authors described an involuntary leaning of the body weight induced by these stimuli.
However, the leaning direction was not dependant on the side where the stimulus was
applied. Independent of the stimulus, amputees reported higher values of RMSv
compared to able-bodied controls, both before and after the stimulus. However, RMSv
was not affected by the stimulus.
1.4.3.3 Single Limb Stance: Amputees vs. Able-bodied Controls.
Hermodsson et al. (1994) evaluated balance during 1-legged stance. In general amputees
failed to maintain an upright position on one leg for 30 seconds on the non-amputated
side (5 out of 18 vascular, 11 out of 18 traumatic amputees). Many of the able-bodied
individuals were also unable to maintain balance on one leg for 30 seconds (19 out of 27
controls). Among all the participants who were able to stand for 30 seconds no significant
differences in COP sway was observed for AP and ML direction when vascular and
traumatic amputees were compared to controls.
When the single-legged stance was performed on the amputated side, almost all of
amputated participants failed to maintain an upright position (16 out of 18 vascular, 12
out of 18 traumatic amputees). Therefore time in balance was the parameter used to
evaluate balance performance in those participants who were not able to stand for 30
seconds. Comparison included the non-amputated limb to the right side of able-bodied
controls and the amputated limb to the left side of able-bodied controls. The analysis of
standing time during single-leg support revealed significant differences between groups.
When comparing all amputees together to able-bodied controls, amputees evidenced
30
significant shorter standing times in both the sound limb and the amputated side. The
comparisons within amputated individuals also showed significant differences, with
reduced standing time in vascular amputees compared to traumatic amputees. When
comparing amputated individuals separately to able bodied controls, significant
differences were described only for vascular amputees with lower standing time values.
Due to the level of difficulty, the single-legged stance assessment under EC condition
was excluded from the study.
31
Chapter 2 – Research Design and Methods
2.1 Rationale, Objectives, and Hypotheses.
2.1.1 Rationale.
Balance performance is one of the parameters evaluated and trained in amputated
individuals. The reductions of balance performance have been reported in various studies
(Hermodsson et al., 1994; Isakov et al., 1992; Nadollek et al., 2002). However there are
many factors associated that can affect balance performance. Sensation information from
mechanoreceptors, exteroceptors and, muscular strength modify the ability to maintain
balance. Some parameters used to evaluate proprioception like TDPM, have displayed
opposite results from different studies (Kavounoudias et al., 2005; Liao & Skinner,
1995). In addition the amputation cause have evidenced that sensation perception could
be modified differently due to amputee’s etiology. Most of the studies evaluated
amputees during double-legged stance and, few studies evaluated the sound limb of
amputees which also indicated changes in muscular strength (Pedrinelli et al., 2002),
changes in proprioception (Kavounoudias et al., 2005; Liao & Skinner, 1995) and altered
balance performance (Hermodsson et al., 1994). Also, to our knowledge, the role of
cutaneous sensation, proprioception, and strength on balance has not been directly
studied in amputees. Based on these studies reports we wanted to evaluate the influence
of cutaneous sensation, proprioception, and muscular strength on balance performance.
Traumatic BKA were used as a model to evaluate and explain the different mechanisms
involved in balance control.
32
2.1.2 Objectives and Hypotheses.
The purpose of this research project was to investigate the role of cutaneous sensation,
proprioception, and strength on balance control in unilateral TTA. In this study, we
evaluated balance during quiet stance and balance after squatting. The specific objectives
were:
• Evaluate the effect of traumatic trans-tibial amputation on: cutaneous sensation,
proprioception, and strength and COP displacement during quiet stance and after balance
perturbation (squats).
Hypothesis number 1: The cutaneous sensation, proprioception and strength in the sound
limb of traumatic TTA are reduced as a consequence of the amputation.
Hypothesis number 2: The COP variables are increased during balance assessment on the
sound limb in traumatic TTA during one-legged quiet standing and after squatting.
• Study the role of cutaneous sensation, proprioception, and strength on balance.
Hypothesis number 3: Reduction in balance in amputees is due at least in part to reduced
cutaneous information, proprioception and strength.
33
Chapter 3 – Research Design and Methods.
3.1 Participants.
Two groups of participants were recruited to contribute in the current study: Seven
traumatic BKA and seven able-bodied individuals. Each group included 6 males and 1
female. Participants' age was lower than 60 years old in order to reduce the effects of
aging process on balance performance. Indeed, according to the results by Buckley et al.
(2002), individuals aged 60 and over show a reduction in balance. Able-bodied healthy
individuals and traumatic BKA were matched for age, sex and level of physical activity.
Traumatic amputees exhibited an age M = 40.1, SD = 10.6 years, height M = 168.5, SD =
9.5 cm and body mass M = 88.4, SD = 22.2 kg. The time since the amputation for
traumatic amputees was M = 42.0, SD = 22.3 months. Amputees with less than 1 year
since the amputation were excluded from the study. The control group showed an age M
= 39.8, SD = 8.1 years, height M = 173.1, SD = 4.7 cm, body mass M = 76.3, SD = 10.8
kg.
Exclusion criteria for both groups were: major visual deficiency, impaired balance or
middle-inner ear pathology or any medical condition that could affect mobility (nervous
deficiency, major cardiac or respiratory disease, motor or cognitive disability), diabetes
mellitus, peripheral vascular disease or any sensorimotor deficit. All the participants read
and signed an informed consent form approved by the ethics committee prior to their
participation in the study.
34
3.2 Balance Assessment.
Balance assessment was conducted during static (quiet standing) and dynamic (squatting)
conditions. Three test conditions were randomly performed, while standing on one leg: 1-
Standing still with EO, 2- Standing still with EC and 3- Squat with EO. Amputated
individuals stood on the sound limb and controls stood on a randomly selected limb while
flexing the contralateral side. The amputated individuals wore their prosthesis during the
whole procedure. The squat maneuver was selected as part of the conditions to evaluate
balance. The knee FLX demanded the motion and the activation of ankle muscles
involved in balance control. On the other hand, the internal disturbance of balance does
not require the use of equipment to produce a perturbation of equilibrium.
The duration for each test trial was set at 45 seconds, and a total of 3 good trials for EO
and up to 5 trials under EC conditions were recorded. We considered a good trial when
the individuals kept the tested limb within the area of assessment of the pressure mat,
without any surface contact with the non-tested limb. In addition to the previous
conditions, during dynamic balance assessment participants were asked to perform a
squat between 30°- 40° of knee FLX then, come up and stay still to consider the test
valid.
As a guide for the squat two dots were placed on the wall at the eye level, 1.5 m in front
of the participant, one when the knees were completely extended and the other dot when
the knee reached 35° of FLX. An electro-goniometer (Noraxon U.S.A. Inc., Scottsdale,
AZ – US) was set on the tested limb to control the amplitude of the squat and to ensure
that participants reached the required knee FLX. The electrogoniometer had two parts;
one was located on the distal portion of the thigh aligned with the longitudinal axis. The
35
second part was placed at the proximal portion of the shank along the longitudinal axis
(Figure 2). There was no measure for the duration of the squats but it was approximately
one second. Participants performed a few trials before the test to ensure they were able to
bend the knee and reach the angle range within the time requested to perform a squat.
Figure 2. Participant on MatScan® system with the electro-goniometer.
3.3 Questionnaires.
The level of physical activity and the level of muscular fatigue were evaluated using
different questionnaires. The assessment of these variables was not part of the main
36
objectives of this research. However, we used this information to ensure that both groups
were matched in terms of level of physical activity and also to avoid the potential
influence of muscular fatigue on balance assessment.
3.3.1 Physical Activity Assessment.
The level of physical activity was evaluated by using two different questionnaires. The
Human Activity Profile (HAP) (Shapiro, 2013) is a self-administered questionnaire that
measures the level of physical activity in healthy and impaired individuals (Polese et al.,
2013; Teixeira-Salmela et al., 1999). The other questionnaire, the Tegner scale is
frequently used to evaluate the level of work, physical activity or sports-related activities
of individuals with knee dysfunction (Gordon et al., 2010; Sonnery-Cottet et al., 2014;
Steadman et al., 2014).
The HAP evaluates the level of physical activity by presenting to the participant a series
of activities with an increasing level of difficulty (Appendix A). The participant checks a
selection-box up to the level of physical activity according to different parameters. These
parameters include the options “Still Doing” if the participant could complete the task
without help. “Have stopped doing this activity” is another option for the person was able
to complete the task before but not at the current time and “Never did this activity” if
never performed the action. The activities include daily life activities from “Getting in
and out of chairs or bed without assistance” to high-performance activities like “Running
or jogging 3 miles in 30 minutes or less”. Two values are calculated from the test. The
Maximum Activity Score (MAS) which is the highest level of activity still performed and
the Adjusted Activity Score (AAS). The AAS results from the subtraction of MAS minus
37
the number of “stopped doing activities” registered below the MAS level. Events marked
as ‘never done’ are not counted (Harbo et al., 2012).
The Tegner score ranges from 0 to 10 (Appendix B). The lowest value indicates “Sick
leave or disability” and the highest value indicates the participation in sports
(“Competitive sports”). The scale considers not only sports activities but also the
individual’s occupation.
3.3.2 Muscular Fatigue.
During the balance assessment, we used the Borg Scale of Global Muscle Fatigue to
evaluate the participants’ perception of fatigue at the lower-limb level (Appendix C). The
fatigue scale ranges from 0 to 10 where 0 means “No fatigue” and 10 means the
maximum level of perceived fatigue (“Very, very strong fatigue”) (Hampton et al., 2014).
The Borg Scale was used during balance assessment at six different moments: one was
previous to starting each condition and one at the end of each condition (Figure 3).
Between each assessment conditions, participants rested for 3 minutes sitting on a chair.
38
Figure 3. Experimental procedures for balance assessment. Participants performed
three random conditions for balance assessment. The Borg scale of global muscle
fatigue was measured six times (T1 to T6), previous to the starting and after the end
of each condition.
3.4 Equipment and Measurements.
During balance assessment we measured COP position. In addition to balance
assessment, we also evaluated three other measures which included: TPS, proprioception,
and muscular strength. The first variables evaluated were related to sensitivity (cutaneous
sensation followed by proprioception), then balance performance, and finally muscle
strength. The purpose of this sequence was to avoid the potential effects of the strength
measurement (soreness, fatigue or pain) on the other variables. All assessments were
performed on the sound limb in amputees and, on a randomly selected limb in able-
bodied controls. Studies have reported differences between the dominant and non-
dominant extremities (Kiss, 2012; Lee et al., 2012; Mezaour et al., 2009). However, it
may be difficult to determine the dominant side in amputees. It is probable that amputees
may have changed the dominant side after the amputation procedure. It is possible that
the amputated extremity was the dominant limb and, the amputees started to use the
39
previously non-dominant limb (sound limb) as the new dominant limb. Due to these
reasons we decided not to match the sides in terms of dominance between the study
group and the participants in the control group. Instead, we randomized the limb
evaluated in the able-bodied participants.
3.4.1 Balance: Center of Pressure.
During both the static and dynamic balance tests, the COP position was recorded using
pressure distribution from a MatScan® System (TekScan, Inc. South Boston, MA, USA)
at a sampling frequency of 100 Hz (Figure 2).This is a portable equipment which is
considered a reliable instrument and can provide objective measurements of the foot
plantar forces and pressures (Zammit et al., 2010).
An electrogoniometer was used to confirm the participants performed the squat within
35±5° of knee FLX. The electrogoniometer activity was recorded with a TeleMyo 2400T
G2 system (Noraxon U.S.A. Inc. Scottsdale, AZ, USA) at a sample rate of 1500 Hz and
synchronized with the MatScan® using the trigger box (Trigger Box -TS-100, MatScan
®).
3.4.2 Cutaneous Sensation: Touch Pressure.
To measure TPS we used Semmes-Weinstein monofilaments (North Coast Medical Inc.
Gilroy, CA. USA). The filaments varied in numbers from 1.65 to 6.65 equating to log 10
of the force in milligrams required to bend the filament. The TPS was registered on two
different sites. The first place evaluated was the tibial site (Figure 4 left panel), 10 cm
below the anterior tibial spine on the medial aspect of the limb. The second site was
40
located under the foot (Figure 4 right panel) on the head of the third metatarsal bone of
the tested limb. The assessment was set in this order due to the skin thickness. The lower
skin thickness at the tibial site facilitated the assessment and made it easier for the
participant to learn the task. The tibial site is considered a pressure-tolerant area
supporting part of amputees’ body while wearing their prosthesis (Lee et al., 2005), and
the plantar site was recommended by the equipment manufacturer as a suggested site to
evaluate foot plantar sensation. Also, these sites were previously studied in amputees
(Kavounoudias et al., 2005) .
Figure 4. Touch pressure sensation. The tibial site (left panel) was located on the
medial aspect of the limb 10 cm below the anterior tibial spine. The plantar sole site
(right panel) was located on the head of 3rd
metatarsal bone.
We used the staircase and the limit methods to evaluate the TPS (Cornsweet, 1962; Jones,
1989). Gross sensation was determined using first the thinnest filament and, continued
with an incremental stimulus until delimiting the threshold stimulus. We stopped when
the individual indicated the perception of pressure sensation from the progressive
stimulus. Using the limits method allowed us to determine a more accurate sensation
measurement. The step size was estimated using three filaments above and three
41
filaments below the threshold filament established by the staircase method (7 filaments in
total). Three ascending/descending series of stimulus followed using these seven
filaments. The test began with the smallest filament (from the group of seven) and
progressively moved up until the participant perceived the touching sensation. We
registered the number of the perceived filament and started the descending series. The
descending series was initiated with the first filament perceived in the previous ascending
series and progressively decreased to the filament exerting a lower pressure. This
procedure continued until the participant did not perceive the touch pressure. The
registered number corresponded to the first filament not perceived in the descending
procedure. The measure continued to the second and third ascending/descending series
using the same set of seven filaments. The recorded measurements from the ascending
and descending steps were used to estimate the level of cutaneous sensation.
The filaments do not require a constant calibration process, which facilitates their use. In
addition, a systematic review by Jerosch-Herold (2005) and a more recent study by
Tracey et al. (2012) suggested that Semmes-Weinstein monofilaments have a high
validity and reliability as a mean to evaluate touch threshold sensation. However, Collins
et al. (2010) suggest that this method is more reliable when measured by a single
researcher.
3.4.3 Proprioception: Joint Threshold Assisted Detection Motion.
To evaluate proprioception we measured the joint threshold assisted detection motion
(TADM) using a custom-made proprioceptive apparatus. This measurement is similar to
the TDPM but it was performed while the participant was bearing the body weight
without hand contact. Under these conditions, the procedure required the body balance
42
control and, the activation of voluntary muscles during the standing position prevented
the displacement of the joints to be fully passive. The device consisted of two platforms,
one was fixed and the other one was mobile. The tested limb (non-amputated side in
amputees and randomly selected side in able-bodied controls) was located on the moving
platform during the assessment. Total body-weight was equally distributed between both
lower extremities with one foot on each platform (Figure 5). Arms were crossed in front
of the chest to avoid the potential bias in joint proprioception from the information that
upper-limb support could provide.
Figure 5. Proprioception machine. The left panel shows the right foot on the fixed
platform attached to a load-cell; the left foot is on the mobile platform. The right
panel shows a position where the mobile platform is up resulting in FLX of the
joints.
43
A load cell was placed under the fixed platform to ensure the equal distribution of the
body weight. We measured first, the force exerted by the total body weight when the
participant stood with feet together on the fixed platform supported by the load cell. The
registered value from the load cell was used as a reference to evenly distribute the body
weight (50 ±10%) between the two platforms when the participant stood placing a foot on
each platform. The platform was randomly displaced up or down from the starting
position of 20° of knee FLX. The platform assisted the joints displacement, moving the
tested knee at a very slow speed of 0.7˚/s, as used in a previous study (Kavounoudias et
al., 2005). Participants were instructed to stop the limb-motion transfer system only when
they perceived the assisted knee joint displacement using an On-Off motor-control
device. In addition, to avoid the potential use of auditory information from the activation
and displacement of the platform, the participants wore a headphone set to hear a white
noise sound while they performed the test. We also prevented the individuals to gather
visual information by covering the top part of the equipment and setting the participants’
position looking straight forward to a distant point on the wall.
Participants performed twelve random trials (6 knee FLX and 6 knee EXT) with at least
10 good trials. A test trial was adequate when the participant maintained the body weight
evenly distributed (50% of the total body weight ±10%). Proprioception was estimated
using the joint angular displacement. The ascending or the descending movements of the
platform during the test involved the displacement of all joints either in FLX or EXT
respectively. Although all the joints were rotated with platform motion, only the knee
angle was computed from the measurement of the vertical linear displacement.
44
Most studies reported that threshold detection of motion is a reliable technique to
evaluate knee proprioception under non-weight bearing conditions (Ageberg et al., 2007;
Arockiaraj et al., 2013; Boerboom et al., 2008; Courtney et al., 2013; Nagai et al., 2012;
Reider et al., 2003); only few studies reported that threshold detection of motion was a
reliable method to measure proprioception under weight-bearing conditions at the knee
(Nagai et al., 2013) and ankle joints (Deshpande et al., 2003).
3.4.4 Muscular Strength: Peak Torque to Body Weight.
We used a KinCom® - KC125AP dynamometer (Chattex Corporation, Chattanooga, TN,
USA) to evaluate muscular strength. The use of the dynamometer allowed us to set and
control a particular combination of contraction and angular speed for muscle strength
measurement. We registered the peak torque and computed the peak torque to body
weight (PT-BW) of concentric FLX /concentric EXT contractions of the knee and ankle
(Figure 6). The knee joint was evaluated before the ankle joint, due to a greater level of
difficulty observed during the pilot test, to perform the test when the ankle joint was
evaluated first. A gravity compensation procedure was performed before each joint
assessment. Setting positions for joint assessment were performed according to the
manufacturer`s manual. To set the tested range of motion, we first evaluated the full
range of motion of the joints and moved back 5° in each direction. Participants were
strapped to the seat during the test in order to reduce the body motion and to obtain the
best performance. They were verbally encouraged to exert their best effort while
performing the test.
45
Figure 6. Muscular strength measurement settings. Knee (top panels) and ankle
(bottom panels).
For the knee joint, individuals were seated with the back reclined at 75˚ and the knee in
90˚ of FLX. To assess the ankle joint the individuals were also seated with the back
reclined at 60˚, and the knee was flexed until the ankle adopted a neutral position. For
both joints assessment, the bottom seat position was elevated at 15° from a horizontal line
46
parallel to the ground level. For each joint, participants had a warm-up set of ten
repetitions at 100˚/second. For the recorded set, the velocity was established at
60˚/second as performed in a previous study (Renstrom et al., 1983b). Participants were
asked to pull and push as hard as possible in concentric FLX and EXT direction for six
complete cycles within the range of motion for each joint.
In general isokinetic dynamometers including the Kin-Com, exhibited the highest level of
validity and reliability for strength measurement. A review of the literature by Nitschke
(1992) supports this statement by analysing several studies that used different isokinetic
dynamometers and settings to evaluate strength.
3.5 Procedures.
All participants first read and signed a consent form previous to the evaluation. We then
evaluated the level of physical activity using the HAP and Tegner questionnaires. We
also registered the record of antecedents to ensure the absence of previous injuries or any
other exclusion criteria.
The first measurement performed was the TPS. We started at the tibial site and then
proceeded to the plantar site. The second test was proprioception. Participants performed
12 random trials, 6 in FLX and 6 in EXT. The next test evaluated was balance
performance during single-leg stance. The test included three randomized trial
conditions: standing still with EO, standing still with EC and balance performance after
squat with EO. During balance assessment, we applied the Borg Scale of Global Muscle
Fatigue before and after each condition. Participants rested for three minutes after each
47
balance condition was tested, to reduce the effect of muscle fatigue on balance
performance. The last evaluation performed was muscular strength. We evaluated first
the knee and then the ankle joint during concentric FLX and concentric EXT
contractions.
3.6 Data Analysis.
To estimate TPS, we calculated the total median value from the three ascending and the
three descending measurements for each tested site. The joint TADM was calculated
using the data from the custom made proprioceptive apparatus. We measured the
difference between the starting position angle (20° of knee FLX) and the knee angle
where the participant perceived the joint displacement, in either knee FLX or knee EXT
direction. The mean threshold for knee FLX or knee EXT was computed from a total of
six trials in FLX and six trials in EXT direction, respectively.
The PT-BW was the measurement used to evaluate muscular strength either in FLX or in
EXT direction. It was recorded over the 6 cycles performed during the test using the Kin-
Com® dynamometer.
For the balance assessment, the MatScan® system indicated the position of the COP for
each measured frame. A period of thirty seconds from the beginning of the stand trials
and after the squats was used to evaluate COP variables. Similar studies that measured
the COP, used recording trial periods which ranged from 30 to 60 seconds (Buckley et
al., 2002; Dornan et al., 1978; Duclos et al., 2009; Duclos et al., 2007; Fernie & Holliday,
1978; Hermodsson et al., 1994; Isakov et al., 1992; Nadollek et al., 2002). We analyzed
48
the COP variables after the squat (not during the test or during the recuperation phase)
because we wanted to evaluate the ‘long-term’ effect of the reactive response to balance
perturbation and also the potential effect of the voluntary muscles anticipatory response
as suggested by Winter (1995). A script allowed us to establish the offset threshold point
during the squat using the electrogoniometer data. The point indicated the angle where
the knee joint reached 5% of the maximum angular speed during knee EXT (Figure 7).
Using the COP data we computed the COPv, RMSd and the RMSv for both the AP and
the ML directions in all the conditions. Some authors consider the velocity as one of the
most reliable methods to measure sway (Cornilleau-Peres et al., 2005; Lafond et al.,
2004; Lin et al., 2008; Raymakers et al., 2005) . Moreover, according to Geurts et al.
(1993), and Pinsault & Vuillerme (2009) RMSv is less affected during EO condition.
These measurements allowed us to analyse independently, the AP and the ML direction
and the potential difference in these two components of the COP variables. Data was
averaged over the 3 recorded trials for each condition and each participant.
The MatScan® system consists of a 50.8 cm per 49.9 cm mat with a matrix of 43.59 cm
per 36.88 cm. The sensel density is 1.4 per cm2 and, a total of 2288 sensels are located in
the matrix. Using a script we were able to do vector analysis decomposition and evaluate
each direction independently for all computed variables.
Using the row sensor and the column sensor position multiplied by the respective row
and column sensor spacing, we determined the exact location of the COP in the matrix
location. This measurement of the COP position in the matrix is indicated in cm for both,
the AP (matrix rows) and the ML (matrix columns) directions. We used the following
formula to compute the COP location for each individual frame:
49
COPi = SLi * SS
where SL = sensor location, SS = sensor spacing and, i is the frame number.
The COPd was computed from the sum of the absolute value of the differences between
the COP locations in the matrix of two consecutive frames in the test. Dividing COPd by
time we were able to obtain COPv.
COPd= ∑ (|COP𝑖+1 − COP 𝑖|)𝑛−1𝑖=1
COPv=COPd
𝑡
where n = total number of frames analyzed and, t= time.
The RMSd and the RMSv were calculated according to the following formulas:
RMSd= √1
𝑛 ∑ (COP𝑖 − COP̅̅ ̅̅ ̅̅ )2𝑛
𝑖=1
2
RMSv= √1
𝑛 ∑ (COPv𝑖 − COPv̅̅ ̅̅ ̅̅ ̅)2𝑛
𝑖=1
2
All of the formulas were used separately for the AP or the ML directions.
In Hermodsson et al. (1994), they analysed the time in balance for those participants who
were not able to keep balance during single-legged stance. Most of the participants in our
study were not able to stand with EC for 45 seconds, but we were not able to determine
the time in balance. For these reasons, we did not analyze standing still condition under
EC.
50
Figure 7. Knee angle during dynamic (squat) balance assessment. The COP analysis
was performed using the data collected for a period of 30 seconds after the end of
the squat (offset point).
3.7 Statistics.
We reported descriptive statistical values for the level of physical activity of all research
participants. Muscular fatigue was analysed using a three-way repeated measures analysis
of variance (ANOVA). We evaluated one between factor (group: amputees/controls) and
two within factors; one factor related to the period of assessment (pre-test/ post-test) and
one factor for all the conditions (standing EO, standing EC and squatting). This analysis
was performed in order to ensure that muscular fatigue did not influence balance results.
Cutaneous sensation was analysed using a two-way repeated measures ANOVA with one
between factor related to the group: amputees/controls and one within factor related to
the tested site: tibial/plantar sole.
51
Proprioception was analysed using a two-way repeated measures ANOVA with one
between factor (group: amputees/controls) and one within factor (direction: FLX/EXT).
We also analysed the PT-BW at knee and ankle joints. Two two-way repeated measures
ANOVA were performed for FLX and EXT strength separately with one between factor
related to group: amputees/controls and one within factor related to joint: knee/ankle.
Two other two-way repeated measures ANOVA analyzed the knee and ankle separately.
The ANOVA included the same between factor related to group (amputees/controls) and
a different within factor related to direction: FLX/EXT.
For strength, we also included the analysis of muscular strength ratios using one two-way
repeated measures ANOVA. This included one between factor related to the group:
amputees/controls and one within factor related to the joint: knee FLX/EXT ratio or ankle
D-FLX/P-FLX ratio.
To analyse the COP variables we performed two-way repeated measures ANOVA. Two
two-way repeated measures ANOVA were related to the direction (AP and ML
separately). The analysis included one between factor related to group
(amputees/controls) and one within factor related to the condition: stand /squat. The other
two two-way repeated measures ANOVA were related to condition (stand and squat
separately). Again, the analysis included one between factor related to group:
amputees/controls and one within factor related to the direction: AP and ML separately.
Pearson’s correlations were performed to evaluate the relationship between cutaneous
sensation, proprioception, muscular strength and balance performance (COPv, RMSv,
RMSd) during quiet standing and after squatting. All the correlations were performed
using the total quantity of participants’ data pooled together.
52
A p-value ≤ 0.05 was used as the evaluation criteria to consider that a variable outcome
evidenced significant differences.
53
Chapter 4 – Results.
In this section we first ensure that the level of physical activity was similar for both
groups and also that muscular fatigue did not affect the evaluation of the different
conditions. We then summarize the results from the different measurements and compare
them between and within groups (means and SD).
4.1 Level of Physical Activity.
The results showed by the HAP questionnaire in amputees evidenced a M = 80.2, SD =
14.8 points and a M = 74.7, SD = 15.7 points for the MAS and the AAS respectively.
Able-bodied participants displayed a M = 93.5, SD = 2.5 points for both, the MAS and
the AAS. The mean level of activity showed by amputees using the Tegner score was M
= 3.0, SD = 1.0 points and, the same test showed a M = 3.8, SD = 1.0 points in controls.
4.2 Level of Muscular Fatigue.
Results for muscular fatigue are presented in Figure 8. The repeated measures ANOVA
indicated no difference between groups (F = 2.30, p = 0.15), conditions (F = 1.29, p =
0.29), or the interactions: condition by group (F = 0.19, p = 0.83), time by group (F =
1.32, p = 0.27), condition by time (F = 0.56, p = 0.58) or condition by time by group (F =
0.99, p = 0.39).
However, the results revealed significant differences for the assessment time (F = 23.71,
p < 0.001). The results evidenced lower values during pre-test conditions (stand EO pre:
M = 1.32, SD = 1.46; stand EC pre: M = 1.07, SD = 1.12; squat pre: M = 1.11, SD = 1.23)
54
compared to post-test values conditions (stand EO post: M = 2.82, SD = 1.61; stand EC
post: M = 2.50, SD = 2.13; squat post: M = 2.11, SD = 1.77).
Figure 8. Mean values of muscular fatigue levels. The figure shows the level of
muscular fatigue for both groups during pre-test and post-test periods for standing
with EO, standing with EC and squat conditions.
4.3 Balance.
Results for balance (COPv, RMSv, and RMSd) are summarized in Figures 9, 10, and 11.
4.3.1 AP and ML Directions.
For the AP direction, no difference was demonstrated for group, condition, or interactions
in COPv, RMSd or RMSv. The COPv evidenced an F = 3.10, p = 0.11 for group, an F =
1.15, p = 0.31 for condition and, for the interaction an F = 0.58, p = 0.46. The RMSd
displayed an F = 1.83, p = 0.20 for group, an F = 0.24, p = 0.63 for condition and, for the
interaction an F = 0.04, p = 0.84. The last one corresponded to the RMSv which
0
1
2
3
4
5
6
7
8
9
10
EO
pre
EO
post
EC
pre
EC
post
SQ
pre
SQ
post
BO
RG
Sca
le
Muscular Fatigue Level
AMP
CTL
55
evidenced an F = 3.68, p = 0.08 for group, an F = 0.01, p = 0.92 for condition and, for the
interaction an F = 0.85, p = 0.82.
When evaluated the ML direction, RMSd showed no difference between groups (F =
1.10, p = 0.32). However, there were significant differences related to group in COPv (F
= 6.73, p = 0.02) and RMSv (F = 6.10, p = 0.03), with higher mean values in COPv in
controls (squat ML: M = 2.81, SD = 0.38 cm/s; stand ML: M = 3.15, SD = 0.57 cm/s)
compared to traumatic amputees (squat ML: M = 2.20, SD = 0.73 cm/s; stand ML: M =
2.15, SD = 0.63 cm/s). Controls also described higher mean values for RMSv (squat ML:
M = 4.49, SD = 1.67 cm/s; stand ML: M = 4.39, SD = 0.93 cm/s) compared to amputees
(squat ML: M = 3.06, SD = 0.99 cm/s; stand ML: M = 3.02, SD = 0.91 cm/s). COPv,
RMSd and RMSv did not report differences related to condition (COPv: F = 1.63, p =
0.23; RMSd: F = 0.002, p = 0.97; RMSv: F = 0.08, p = 0.79) or group by condition
interaction for the ML direction (COPv: F = 4.23, p = 0.06; RMSd: F = 0.76, p = 0.40;
RMSv: F = 0.002, p = 0.97).
4.3.2 Standing and Squatting.
Other comparisons for COP variables included the separate evaluation of the conditions
(standing and squatting). The results revealed no difference between groups for the squat
condition (COPv: F = 3.57, p = 0.09; RMSd: F = 1.64, p = 0.23; RMSv: F = 3.10, p =
0.11) nor the stand condition (COPv: F = 3.20, p = 0.10; RMSd: F = 0.87, p = 0.37;
RMSv: F = 1.98, p = 0.18).
56
However, all COP variables displayed significant differences related to the AP and ML
directions under the squat condition (COPv: F = 4.79, p = 0.05; RMSd: F = 36.47, p <
0.001; RMSv F = 8.50, p = 0.01). The squat condition in AP direction revealed higher
mean values of COPv (M = 2.83, SD = 0.94 cm/s), RMSd (M = 0.72, SD = 0.15 cm) and
RMSv (M = 5.02, SD = 2.78 cm/s) when compared to squat ML direction (COPv: M =
2.53, SD = 0.63 cm/s; RMSd: M = 0.60, SD = 0.11 cm; RMSv: M = 3.83, SD = 1.54
cm/s). The direction effect for the stand condition evidenced similar results but, revealed
significant differences only for the RMSd (F = 23.46, p < 0.01) and the RMSv (F = 6.42,
p = 0.03). The stand AP direction exhibited higher mean values (RMSd: M = 0.75, SD =
0.21 cm; RMSv: M = 5.19, SD = 2.78 cm/s) compared to stand ML direction (RMSd: M
= 0.60, SD = 0.14 cm; RMSv: M = 3.71, SD = 1.14 cm/s). Despite revealing no difference
in COPv values (F = 4.46, p = 0.06) between AP and ML directions, the results indicated
a trend to significant higher mean values in the AP direction (M = 3.20, SD = 1.39 cm/s)
compared to the ML direction (M = 2.68, SD = 0.78 cm/s).
The interaction direction by group also indicated significant differences only for the squat
condition in the RMSd (F = 5.62, p = 0.04) but not for COPv (F = 0.74, p = 0.40) or
RMSv (F = 1.52, p = 0.24). Controls evidenced higher mean values (squat AP: M = 0.78,
SD = 0.18 cm; squat ML: M = 0.61, SD = 0.14 cm) when compared to amputated
individuals (squat AP: M = 0.65, SD = 0.07 cm; squat ML: M = 0.57, SD = 0.14 cm). For
the stand condition, the interaction direction by group did not report significant
differences for any of the COP variables (COPv: F = 0.12, p = 0.73; RMSd: F = 0.01, p =
0.91; RMSv F = 0.002, p = 0.96).
57
Figure 9. Mean values of the COPv for AP and ML direction during dynamic
(squat) and static (stand) conditions with EO. Significant differences between
amputees and able-bodied controls were evidenced only for the ML direction.
Figure 10. Mean values of the RMSv for AP and ML direction during dynamic
(squat) and static (stand) conditions with EO. Significant differences between
amputees and able-bodied controls were evidenced only for the ML direction.
0
2
4
6
Squat
AP
Stand
AP
Squat
ML
Stand
ML
CO
P V
elo
city
(cm
/s)
Mean Value of
Center of Pressure Velocity
AMP
CTL
0
6
12
Squat
AP
Stand
AP
Squat
ML
Stand
ML
RM
S V
eloci
ty (
cm/s
)
Mean Value of RMS Velocity
AMP
CTL
58
Figure 11. Mean values of the RMSd for AP and ML direction during dynamic
(squat) and static (stand) conditions with EO. No significant differences were
observed between amputees and able-bodied controls.
4.4 Cutaneous Sensation.
Figure 12 displays the TPS values for both groups at both the tibial and plantar sites,
presented as a number representing the force in grams (log10) required to bend the
filament. No difference was described related to group (F = 1.40, p = 0.26), site (F =
2.52, p = 0.14) or site by group interaction (F = 2.23, p = 0.16).
4.5 Proprioception.
The mean values of the knee angular displacement during proprioception assessment are
presented in Figure 13. No difference in mean proprioception values were evidenced
0.0
0.5
1.0
1.5
Squat
AP
Stand
AP
Squat
ML
Stand
ML
RM
S D
isp
lace
men
t (c
m)
Mean Value of RMS Displacement
AMP
CTL
59
related to the group (F = 0.34, p = 0.57), direction (F = 0.78, p = 0.40) or the direction by
group interaction (F = 0.71, p = 0.42).
Figure 12. Median values of TPS thresholds at tibial and plantar sites.
Figure 13. Mean values for knee angular displacement measurements during FLX
and EXT motion for the proprioception procedure.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Tibial Site Plantar Site
Pre
ssu
re T
hre
sho
ld (
Lo
g 1
0 -
mg
)
Touch Pressure Sensation Threshold AMP
CTL
0
1
2
3
FLX EXT
Δ A
ng
le o
f D
etec
tio
n (
deg
rees
)
Proprioception Threshold
AMP
CTL
60
4.6 Muscular Strength.
Figure 14 shows the strength values for knee and ankle joints in FLX and EXT directions
for both, traumatic amputees and able-bodied controls. When evaluating separately the
strength at the knee and at the ankle joints, the study revealed no difference between
groups in both joints (knee: F= 0.81, p = 0.39; ankle: F = 1.30, p = 0.28). Similar results
were described for the interaction direction by group with no difference revealed for both
joints (knee: F = 1.0, p = 0.34; ankle: F= 0.008, p = 0.93). However the direction effect
evidenced significant differences at the knee (F = 9.8, p = 0.01) and at the ankle joint (F
= 16.68, p = 0.002). The knee displayed a higher mean PT-BW for EXT muscles (M =
1.52, SD = 0.29 N/Kg) compared to knee FLX (M = 1.17, SD = 0.39 N/Kg). At the ankle
joint similar results were described, and P-FLX muscles showed higher PT-BW (M =
0.72, SD = 0.27 N/Kg) as compared to ankle D-FLX muscles which revealed lower mean
values (M = 0.56, SD = 0.21 N/Kg).
When evaluating separately the directions, the study revealed no difference between
groups, neither for the FLX (F = 2.27, p = 0.16) nor EXT (F = 0.40, p = 0.54) direction.
No differences were described for the joint by group interaction (FLX: F= 0.16, p = 0.69;
EXT: F = 0.95, p = 0.35). However, the results evidenced significant difference for joint
effect. They displayed an F = 13.26 (p = 0.03) for joint FLX and, an F = 257.75 (p <
0.001) for joint EXT muscles. Knee FLX (M = 1.17, SD = 0.39 N/Kg) and knee EXT (M
= 1.52, SD = 0.29 N/Kg) muscles showed significant higher values than ankle D-FLX (M
= 0.56, SD = 0.21 N/Kg) and ankle P-FLX (M = 0.72, SD = 0.27 N/Kg) muscles
respectively.
61
Figure 14. Mean values of the PT-BW at the knee and the ankle during isokinetic
concentric FLX and EXT.
Figure 15. Mean values of the ratios for knee and ankle FLX/EXT muscles during
isokinetic concentric motion.
0.0
0.5
1.0
1.5
2.0
Knee
FLX
Knee
EXT
Ankle
D-FLX
Ankle
P-FLX
Pea
k t
orq
ue
to b
od
y w
eig
ht
(Nm
/Kg
)
Muscular Strength Peak-Torque to Body Weight
AMP
CTL
0.00
0.50
1.00
1.50
Knee Ratio
FLX/EXT
Ankle Ratio
D-FLX/P-FLX
Ra
tio
Fle
xo
r/E
xte
nso
r M
usc
les
Peak Torque to Body Weight Ratios
AMP
CTL
62
Strength ratios are presented in Figure 15. When comparing joints’ ratios, the results
revealed no difference related to group (F = 1.40, p = 0.26), joint (F = 0.002, p = 0.97) or
the joint by group interaction (F = 0.84, p = 0.38).
4.7 Correlations.
Pearson correlations were performed between COP variables and the other variables that
could potentially affect balance. All the correlations performed between COP and all the
study variables (TPS, proprioception, and muscular strength) are presented in Appendix
D and the correlation graphs in Appendix E (Tables 3, 4, 5). Pearson coefficients
revealed significant correlation levels for muscular strength, in particular ankle strength
for the P-FLX direction and, strength ratios. Table 2 summarizes the coefficients that
evidenced significant statistical values (p ≤ 0.05) or a trend to significant correlations.
COP Variable Condition Pearson Correlation p-value
COPv
TPS tibial site Squat AP 0.54 0.06†
Ankle P-FLX
Squat AP 0.64 0.02
Squat ML 0.60 0.03
Stand AP 0.70 0.01
RMSd Ankle P-FLX Squat AP 0.63 0.02
Stand AP 0.53 0.05
RMSv
Knee FLX/EXT ratio
Stand AP 0.52 0.06†
Stand ML 0.53 0.06†
Squat AP 0.55 0.06†
Squat ML 0.61 0.03
Ankle P-FLX Stand AP 0.68 0.01
Ankle D-FLX/P-FLX ratio Squat AP -0.58 0.04
Squat ML -0.61 0.03
Table 2. Significant correlations between the COP (COPv, RMSd, RMSv) and other
variables. († non-significant difference).
63
Chapter 5 – Discussion.
The first goal of our study was to evaluate cutaneous sensation, proprioception, muscular
strength, and balance in the non-amputated side of TTA compared to a randomly selected
limb in able-bodied controls; the second was to use the amputation condition as a model
to evaluate the role of cutaneous sensation, proprioception and muscular strength on
balance performance. In our study, the only variable that showed differences between
groups was balance. Amputees demonstrated reduced values in COPv and RMSv
compared to able-bodied controls for ML direction.
The other variable that evidenced significant differences was muscular strength, but these
differences were related to the joint and direction tested. The results displayed lower
strength level at the ankle joint compared to the knee and also reduced muscular strength
in knee FLX and ankle D-FLX compared to knee EXT and ankle P-FLX muscles
respectively. As for correlations the main variable that indicated a relationship with
balance was muscular strength predominantly at the ankle level, and strength ratios.
Given the results obtained from our study, we are able to suggest that the differences
displayed between groups for the variables of COP are best explained by muscular
strength. However, given the fact that our study does not contain a large number of
participants, the aforementioned suggestion may not necessarily fully explain this
difference.
64
5.1 Balance.
As hypothesized, balance was affected in amputees in our study. The loss of information
from anatomical structures demanded several adaptations on different systems in order to
maintain balance. As a result, we expected an increment of COP variables in amputees.
Our expectation for reduced balance was also based in part on the existing literature. An
increase in amputees’ COP variables was described by diverse studies during double-
legged stance (Buckley et al., 2002; Dornan et al., 1978; Fernie & Holliday, 1978; Geurts
et al., 1991; Hermodsson et al., 1994; Isakov et al., 1992; Nadollek et al., 2002). Various
studies also associated the reduction of COPv (Le Clair & Riach, 1996) as well as RMSd
and RMSv (Geurts et al., 1993) with better balance performance.
The results that we present for COP variables are opposed to the ones proposed in our
hypothesis. Although we expected increments of the COP variables in amputees based on
the results that similar studies reported in the literature, we described reduced values of
COP variables in TTA when compared to able-bodied controls. It should be noted
however that our study was performed during single-legged stance on the non-amputated
side. In our study it is possible that the greater use and greater reliance of the non-
amputated side on a daily basis in TTA could lead to a greater stability. The non-
amputated side may therefore be more stable and strong. The increment in AP direction
for COP excursion on the sound limb side compared to the amputated side during double-
legged stance (Nadollek et al., 2002) may be related to the trend described in amputees to
displace their body weight to the non-amputated side (Duclos et al., 2009; Duclos et al.,
2007; Engsberg et al., 1992; Isakov et al., 1992).
65
To our knowledge, only Hermodsson et al. (1994) compared single-legged stance on the
non-amputated limb of TTA to able-bodied controls. Despite not reporting differences in
COP amplitude for AP and ML directions on the non-amputated limb, the authors
revealed significant shorter time in balance for all amputees together when compared to
able-bodied controls. Vascular amputees in particular showed significant shorter standing
time when compared alone to able-bodied, or when compared to traumatic amputees. It is
possible that the sound limb of traumatic amputees in our study was not as affected as
those of vascular amputees described by Hermodsson’s study.
It should be noted that, similar to our study, a greater mean surface of sway has been
displayed in able-bodied controls when compared to traumatic and non-traumatic
amputees (Gauthier-Gagnon et al., 1986). Despite revealing lower values of mean sway
surface and a greater ABS, amputees used only a small proportion of the ABS (0.3%)
compared to the proportion used by able-bodied controls (2%). According to the authors,
this proportion of the ABS represents the area of stability, and therefore a lower
proportion of use of this area could be interpreted as a less stable condition. In addition to
this, a reduction in the activity of muscles about the ankle joint has been associated with a
reduction in postural sway (Gurfinkel et al., 1995; Gurfinkel et al., 1979). This result may
also explain in part, why lower values in COP variables do not necessarily indicate a
better balance performance. There are similar results showed within a study by Davids et
al. (1999), where individuals with anterior cruciate ligament injury displayed lower COP
variables compared to controls. We should also consider the idea proposed by Duclos et
al. (2009) suggesting that the CNS uses this strategy as a mechanism to obtain more
information for balance control.
66
The study presented by Buckley et al. (2002) also included double-legged stance, but
instead they performed a dynamic balance assessment using a stabilimeter. In our study,
we also evaluated dynamic balance. However, we studied COP variables (COPv, RMSd
and RMSv) and different conditions (squatting during single-legged stance). In the study
by Buckley et al. (2002), reduced values for time in balance in TTA compared to controls
was reported, meaning amputees were less stable during dynamic balance assessment.
The other variables measured in Buckley’s study demonstrate that the differences in the
number of board contacts were only significant for ML direction under blindfolded
conditions, with more board contacts on the amputated side. Despite the absence of
differences, related to the groups, the size effect suggested a trend to higher mean time of
board contacts for AP condition (Buckley et al., 2002).
5.2 Cutaneous Sensation.
In our study, cutaneous sensation did not reveal differences related to group, site or site
by group interaction. However, other studies such as Kosasih & Silver-Thorn (1998),
and Kavounoudias et al. (2005) reported reduced levels of sensation in amputees. Both
Kavounoudias et al. (2005) and Kosasih & Silver-Thorn (1998) compared the amputated
side to the non-amputated side. However, only Kavounoudias et al. (2005) compared
sensation of the non-amputated to able-bodied control group.
In our study, we used the same sites and methods as Kavounoudias et al. (2005) to assess
TPS. The absence of differences between groups in our study may be associated with the
fact that Kavounoudias et al. (2005) evaluated amputees from traumatic and non-
67
traumatic etiologies. It is described that amputations related to diabetes and vascular
diseases are the most frequent etiologies of non-traumatic amputations which frequently
exhibit an altered cutaneous sensitivity. These diseases also lead to the concomitant
development of sensory neuropathy which can influence not only cutaneous sensation but
also proprioception (van Deursen & Simoneau, 1999). However, when Kavounoudias et
al. (2005) compared vascular and traumatic amputees separately, they reported that only
traumatic amputees showed significant higher TPS values specifically at the plantar site.
5.3 Proprioception.
The assessment of proprioception in our study did not demonstrate differences between
groups, directions or direction by group interaction. This does not correspond to our
expectations and to some of the existing studies (Eakin et al., 1992; Kavounoudias et al.,
2005; Liao & Skinner, 1995). These studies described reductions in proprioceptive
information in amputees. Eakin et al. (1992), Kavounoudias et al. (2005) and, Liao &
Skinner (1995) measured proprioception in LLA from diverse etiologies and levels (AKA
and BKA or BKA alone) using different settings (seated or standing) and various speeds
which, ranged from 0.4°/second to 0.7°/second.
Eakin et al. (1992) and Liao & Skinner (1995) reported higher TDPM values in the
amputated limb compared to the non-amputated limb. These results are opposite to those
of Kavounoudias et al. (2005), who reported non-significant differences in TDPM.
Similar to our study, Liao & Skinner (1995) and Kavounoudias et al. (2005) compared
the non-amputated side to controls. Both of them revealed higher TDPM in the non-
68
amputated side compared to able-bodied controls. Liao & Skinner used a speed of 0.4°/s
and pooled traumatic and vascular amputees, which may have led to different results.
However, Kavounoudias et al. (2005) used the same speed as in our study (0.7°/s) and
evaluated vascular and traumatic amputees separately. Their results indicated higher
TDPM values on the non-amputated side at the knee, but not at the ankle joint for both,
traumatic and vascular amputees when compared to controls. The absence of difference
for proprioception in our study may be related to the settings used in our experiment. In
our study we evaluated the level of proprioception using TADM, a procedure similar to
the TDPM. Note that Kavounoudias et al. (2005) performed their evaluation while the
participants were seated while we performed the assessments with the participants
bearing their body-weight. The amputated individuals from our study may have perceived
much faster the joint displacement due to the weight-bearing condition because of the
related “pre-activation” of different muscles involved in balance control during double-
legged stance. It is possible that the participants also obtained proprioceptive information
from the activation of different muscles involved in balance maintenance. Also, the
procedure in our study implied the displacement of multiple joints: the ankle, the knee
and the hip. All these structures could provide proprioceptive information and may
explain the absence of differences in our study. Also, the fact that the standing position is
more challenging for the balance system may have influenced the results.
69
5.4 Muscular Strength.
When we evaluated muscular strength, our results revealed no significant difference
between the groups. This is not what we expected and is different from other studies
which showed a reduction in muscular strength in amputees.
Studies that compared the amputated side to the non-amputated side reported reduced
muscular strength in the amputated side (Isakov et al., 1996b; Moirenfeld et al., 2000;
Pedrinelli et al., 2002). The aforementioned result suggests that muscular strength might
not be affected in the non-amputated limb.
We have considered the possibility of “a training effect”. It has been reported that
amputees support more body-weight on the non-amputated side (Duclos et al., 2009;
Duclos et al., 2007; Gauthier-Gagnon et al., 1986; Isakov et al., 1992). The second reason
could be the level of physical activity. Although it was not part of the main objectives of
this study, we evaluated the level of physical activity. The participants in our research
were classified as physically active according to the AAS scale in the HUMAP
questionnaire. The increased, constant use of the non-amputated limb may have an effect
on muscular strength in amputees resulting in smaller or no difference between the non-
amputated extremity and the selected limb assessed in the able-bodied-control group.
Note, however that Pedrinelli et al. (2002) not only compared the amputated side to the
non-amputated side from different etiologies. They also evaluated muscular strength on
the non-amputated side in amputees and compared it to that of able-bodied controls. In
their study, they described a reduction in muscular strength of the non-amputated side.
Pedrinelli et al. (2002) recruited traumatic and non-traumatic amputees to evaluate
70
various parameters. Testing two different speeds, they evaluated muscular strength and
muscular resistance. They used a set of 4 repetitions at the speed of 60°/second to
evaluate muscular strength. They also tested 6 from a maximum of 20 repetitions at a
speed of 180°/second, to evaluate muscular resistance. All of the measurements were
relative to concentric/concentric contractions during knee FLX and EXT direction. It is
possible that the different settings used by Pedrinelli might be more sensitive to the
amputation. In addition, Pedrinelli et al. (2002) included amputees from mixed etiologies
in their study and we included only amputees from traumatic origin. The inclusion of
vascular amputees in Pedrinelli’s study may have led to the decrease in strength reported
in amputees.
5.5 Correlations.
For correlations, we evaluated the role of cutaneous sensation, proprioception and
muscular strength on balance performance. To our knowledge, the literature has not
reported any studies that compared at the same time TPS, proprioception and muscular
strength against performance in tasks involving balance.
In our study, the only variable that revealed significant correlations with the COP was
muscular strength, predominantly about the ankle joint. The increments in COP variables
and, the level correlation between COP variables and muscular strength at the ankle level
allow us to suggest the importance of muscle strength at the ankle in balance
maintenance. It seems also important to keep an adequate balance between D-FLX and
P-FLX muscles. The ankle strategy is one of the most important mechanisms involved in
71
balance maintenance (Winter, 1995, 2009; Winter et al., 1990) and muscular strength
changes may explain in part the variations in balance performance.
We did not report significant correlations between TPS, proprioception and balance. A
possible explanation could be an adaptation of the CNS, similar to that proposed for
balance (Duclos et al., 2009). The CNS might use the proprioceptive information from
the remaining receptors in the amputated extremity and the information originated from
the receptors in the sound limb to compensate the proprioception deficit. Another
possibility is related to the sample size. These factors might probably influence the
statistical analysis and the determination of correlations among the variables.
The correlations between strength and COP variables should be taken carefully due to the
controversial interpretations of COP variables (Palmieri et al., 2002). Considering the
studies where reduced COP variables indicate a greater postural control (Baier & Hopf,
1998; Baloh et al., 1998; Davids et al., 1999; Geurts et al., 1993; Le Clair & Riach,
1996), a positive correlation will display a less stable condition when muscular strength
increases. On the other hand, if we consider the study by Davids et al. (1999), the same
correlation for muscular strength will indicate that muscular strength increments would
be associated to a more stable position during postural challenge. This correlation seems
to be apparently more logical. Moreover, individuals with greater strength levels may
increase the oscillation levels in order to have a better control of their balance.
72
Chapter 6. Limitations.
In our study, we did not include the limb dominance as a parameter to evaluate balance in
TTA. Not considering the limb dominance is a limitation for our study. We omitted this
factor due to the possibility that it could have been affected by the amputation. We
considered different scenarios including one where the dominant limb may have been
amputated. As a result and subsequent to surgery, the individuals could have started to
use the non-amputated limb as a dominant limb. This situation could mislead the results
related to the limb dominance.
The evaluation of proprioception was performed under assisted conditions. The
parameters of evaluation demanded participants to support their body weight during the
proprioception task. Keeping the body in an upright position involves a coordinated
action of various muscle groups. Thus, we can consider that there is a “pre-activation”
response of the muscles during the evaluation of proprioception. This “pre-activation”
can also modify the assessment of proprioception during joints’ displacement. In
addition, during proprioception assessment, the test was performed without hand contact
on the support. We chose this position because we did not want participants to hold part
of their body weight, even though the standing position also involved a balance task. The
purpose of these settings was to evaluate proprioception under a condition the closest to a
real life situation where the proprioception information is more relevant during an upright
position which demands a higher level of muscular activation.
We consider the total number of participants in the current study as a limitation. We were
able to match only seven TTA, which volunteered to participate in the study. The limited
number of participants restricted the possibility to perform additional statistical tests to
73
measure the potential effect of other factors. In addition, the absence of differences could
be due to a reason other than that specified in the hypothesis. An unknown process may
underlie the relationship between COP measurements and the other variables.
If we could repeat the study, it would be ideal to include the evaluation of amputees in
different periods of the rehabilitation process to evaluate the effect of this intervention on
balance performance.
74
Chapter 7 – Conclusions.
Balance and postural control are considered a multifactorial condition. Different studies
have included the assessment of cutaneous sensation, proprioception, and muscular
strength separately.
Our study reports a reduction of different COP parameters in amputees and changes in
muscular strength related to the direction of the assessment. Reductions of COPv and
RMSv in amputees were shown to be significant particularly for the ML direction,
contrary to most studies that reported increments in COP variables when amputees were
compared to able-bodied controls. It is possible that the reduced COP values are due in
part to the fact that amputees rely more on their sound limb on a day-to-day basis during
ambulation and standing. Yet, reduced values of COP variables do not necessarily
indicate an increase in balance performance.
The correlations for COP variables mainly related to muscular strength, in particular to
ankle strength, indicating the influence of muscle strength in balance performance.
However, we can assume that this correlation is logical only if the increase in COP
variables indicates an increased balance.
Based on our results and also on the literature review we can state the importance of a
muscle strengthening program. This program must be accompanied by activities of body-
weight translation and body weight control to distribute as evenly as possible, the body
weight between both extremities.
75
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84
Appendix A Human Activity Profile
Human Activity Profile
85
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Instructions:
This brochure contains elements describing tasks of daily life.
Read each statement and mark an X in the column indicating either
you are Still Doing This Activity, you Have Stopped Doing This
Activity or Never Did this task. Use the following instructions to
guide you in your choice of responses:
Draw an X in the column that “Still Doing” if you have
completed this task without help the last time or opportunity
you have had need.
Draw an X in the column “Have stopped doing this activity”
if you have completed the task in the past but would not be able
to do the same today if you have the chance.
Draw an X in the column “Never did this activity” if you've
never undertaken this task.
86
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Please mark one of the three spaces for each column according to your activity profile
Still Doing
This Activity
Have Stopped
Doing This
Activity
Never Did
This Activity
1. Getting in and out of chairs or bed (without
assistance)
2. Listening to the radio
3. Reading books, magazines, or newspapers
4. Writing (letters, notes)
5. Working at a desk or table
6. Standing (for more than 1 minute)
7. Standing (for more than 5 minutes)
8. Dressing or undressing (without assistance)
9. Getting clothes from drawers or closets
10. Getting in or out of a car (without assistance)
11. Dining at a restaurant
12. Playing cards/table games
13. Taking a bath (no assistance needed)
14. Putting on shoes, stockings, or socks (no rest
or break needed)
15. Attending a movie, play, church event, or
sports activity
16. Walking 30 yards (27 meters)
17. Walking 30 yards (nonstop)
18. Dressing/undressing (no rest or break
needed)
19. Using public transportation or driving a car
(99 miles or less)
20. Using public transportation or driving a car
(100 miles or more)
21. Cooking your own meals
22. Washing or drying dishes
87
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Please mark one of the three spaces for each column according to your activity profile
Still Doing
This Activity
Have Stopped
Doing This
Activity
Never Did
This Activity
23. Putting groceries on shelves
24. Ironing or folding clothes
25. Dusting/polishing furniture or polishing a car
26. Showering
27. Climbing 6 steps
28. Climbing 6 steps (nonstop)
29. Climbing 9 steps
30. Climbing 12 steps
31. Walking ½ block on level ground
32. Walking ½ block on level ground (nonstop)
33. Making a bed (not changing sheets)
34. Cleaning windows
35. Kneeling, squatting to do light work
36. Carrying a light load of groceries
37. Climbing 9 steps (nonstop)
38. Climbing 12 steps (nonstop)
39. Walking ½ block uphill
40. Walking ½ block uphill (nonstop)
41. Shopping (by yourself)
42. Washing clothes (by yourself)
43. Using public transportation or driving a car
(100 miles or more)
44. Cooking your own meals
45. Washing or drying dishes
46. Putting groceries on shelves
47. Ironing or folding clothes
88
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Please mark one of the three spaces for each column according to your activity profile
Still Doing
This Activity
Have Stopped
Doing This
Activity
Never Did
This Activity
48. Dusting/polishing furniture or polishing a car
49. Showering
50. Climbing 6 steps
51. Climbing 6 steps (nonstop)
52. Climbing 9 steps
53. Climbing 12 steps
54. Walking ½ block on level ground
55. Walking ½ block on level ground (nonstop)
56. Making a bed (not changing sheets)
57. Cleaning windows
58. Kneeling, squatting to do light work
59. Carrying a light load of groceries
60. Climbing 9 steps (nonstop)
61. Climbing 12 steps (nonstop)
62. Walking ½ block uphill
63. Walking ½ block uphill (nonstop)
64. Shopping (by yourself)
65. Washing clothes (by yourself)
66. Walking 1 block on level ground
67. Walking 2 blocks on level ground
68. Walking 1 block on level ground (nonstop)
69. Walking 2 blocks on level ground (nonstop)
70. Scrubbing (floors, walls or cars)
71. Making a bed (changing sheets)
72. Sweeping
73. Sweeping (5 minutes nonstop)
74. Carrying a large suitcase or bowling (one
game)
75. Vacuuming carpets
89
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Please mark one of the three spaces for each column according to your activity profile
76. Vacuuming carpets (5 minutes nonstop)
77. Painting (interior/exterior)
78. Walking 6 blocks on level ground
79. Walking 6 blocks on level ground (nonstop)
80. Carrying out the garbage
81. Carrying a heavy load of groceries
82. Climbing 24 steps
83. Climbing 36 steps
84. Climbing 24 steps (nonstop)
85. Climbing 36 steps (nonstop)
86. Walking 1 mile
87. Walking 1 mile (nonstop)
88. Running 110 yards (100 meters) or playing
softball/baseball
89. Dancing (social)
90. Doing calisthenics or aerobic dancing (5
minutes nonstop)
91. Mowing the lawn (power mower, but not a
riding mower)
92. Walking 2 miles
93. Walking 2 miles (nonstop)
94. Climbing 50 steps (2 ½ floors)
95. Shoveling, digging, or spading
96. Shoveling, digging, or spading (5 minutes
nonstop)
97. Climbing 50 steps
98. Walking 3 miles or golfing 18 holes without
a riding cart
99. Walking 3 miles (nonstop)
100. Swimming 25 yards
101. Swimming 25 yards (nonstop)
90
HUMAN ACTIVITY PROFILE
Code: ________________________________________ Date: ____________________
Please mark one of the three spaces for each column according to your activity profile
Still Doing
This Activity
Have Stopped
Doing This
Activity
Never Did
This Activity
102. Bicycling 1 mile
103. Bicycling 2 miles
104. Bicycling 1 mile (nonstop)
105. Bicycling 2 miles (nonstop)
106. Running or jogging ¼ mile
107. Running or jogging ½ mile
108. Playing tennis or racquetball
109. Playing basketball/soccer (game play)
110. Running or jogging ¼ mile (nonstop)
111. Running or jogging ½ mile (nonstop)
112. Running or jogging 1 mile
113. Running or jogging 2 miles
114. Running or jogging 3 miles
115. Running or jogging 1 mile in 12 minutes or
less
116. Running or jogging 2 miles in 20 minutes or
less
117. Running or jogging 3 miles in 30 minutes or
less
91
HUMAN ACTIVITY PROFILE
David M Daughton, M.S. and A. James Fix, Ph.D.
Code: _____________________________ Date: _______________________
Age: ____________ Gender: M or F
HAP SUMMARY SCORE GRID
Primary Score Score Percentile
MAS
AAS
Activity Age
Fitness
Classification
Low _____ Fair _____ Average & Above _____
Activity
Classification
Impaired _____ Moderately Active ____ Active _____
Energy Analysis Score Percentile
EEP
LEC
Dyspnea Scale
92
Appendix B Tegner Activity Score
Tegner Activity Score
93
TEGNER ACTIVITY SCORE
Check the box beside the activity which best describes the level at which the patient
participates. (Please check only one box).
Level 10 Competitive sports: Soccer – national & international elite
Level 9 Competitive sports: Soccer – lower divisions, Ice hockey, Wrestling and/or
Gymnastics
Level 8 Competitive sports: Squash or badminton, Athletics (jumping, etc.) and/or
Downhill skiing
Level 7
Competitive sports: Tennis, Athletics (running), Motocross/speedway,
Handball and/or Basketball
OR Recreational sports: Soccer, Ice hockey, Squash, Athletics (jumping,
etc.) and/or Cross-country track
Level 6 Recreational sports: Tennis/badminton, Handball, Basketball, Downhill
skiing and/or Jogging at least 5X per week
Level 5
Work: Heavy labor (e.g., Building, Forestry)
OR Competitive sports: Cycling or Cross-country skiing
OR Recreational sports: Jogging on uneven ground at least twice weekly
Level 4
Work: Moderately heavy labor (e.g., Truck driving, Heavy domestic work)
OR Recreational sports: Cycling, Cross-country skiing, and/or Jogging on
even ground at least twice weekly
Level 3
Work: Light labor (e.g., Nursing)
OR Competitive and Recreational Swimming
OR Walking in forest possible
Level 2 Work: Light labor
OR Walking on uneven ground possible but impossible to walk in forest
Level 1 Sedentary work
OR Walking on even ground possible
Level 0 Sick leave or disability because of knee problems
94
Appendix C Modified Borg Scale
Modified Borg Scale
95
Modified Borg Scale
0 Nothing at all
0.5 Extremely weak (just noticeable)
1 Very weak
2 Weak (light)
3 Moderate
4 Somewhat strong
5 Strong (heavy)
6
7 Very strong
8 8
9 9
10 Extremely strong (almost max)
96
Appendix D Pearson Correlation
Coefficients
Pearson Correlations Coefficients
97
Variable Pearson
Correlation Squat AP Squat ML Stand AP Stand ML
TPS tibial CC 0.54 0.49 0.29 0.39
p-Value 0.05 0.09 0.31 0.16
TPS plantar CC -0.11 -0.16 0.06 -0.08
p-Value 0.72 0.59 0.83 0.78
Proprioception FLX CC 0.26 0.31 0.29 0.24
p-Value 0.42 0.33 0.34 0.43
Proprioception EXT CC -0.15 -0.08 -0.20 -0.14
p-Value 0.65 0.80 0.51 0.65
Knee PTBW FLX CC 0.32 0.18 0.43 0.34
p-Value 0.28 0.55 0.12 0.24
Knee PTBW EXT CC 0.36 0.18 0.44 0.08
p-Value 0.23 0.55 0.12 0.77
Ankle PTBW P-FLX CC 0.64 0.60 0.70 0.45
p-Value 0.02 0.03 0.01 0.10
Ankle PTBW D-FLX CC 0.52 0.49 0.49 0.39
p-Value 0.07 0.09 0.07 0.17
Knee PTBW FLX/EXT
ratio
CC 0.16 0.11 0.18 0.32
p-Value 0.60 0.72 0.54 0.26
Ankle PTBW
D-FLX/P-FLX ratio
CC -0.14 -0.13 -0.30 -0.20
p-Value 0.66 0.67 0.29 0.48
Table 3. Pearson correlations between COPv and other variables under the squat
and the stand conditions for AP and ML direction.
98
Variable Pearson
Correlation Squat AP Squat ML Stand AP Stand ML
TPS tibial CC 0.10 0.03 0.25 0.32
p-Value 0.74 0.91 0.38 0.26
TPS plantar CC -0.05 -0.12 0.20 0.24
p-Value 0.86 0.70 0.49 0.40
Proprioception FLX CC 0.11 -0.06 0.29 0.27
p-Value 0.73 0.85 0.34 0.37
Proprioception EXT CC -0.13 -0.09 0.01 -0.10
p-Value 0.69 0.79 0.96 0.75
Knee PTBW FLX CC 0.29 0.00 0.40 0.41
p-Value 0.34 0.99 0.15 0.15
Knee PTBW EXT CC 0.07 -0.35 0.30 -0.02
p-Value 0.81 0.24 0.30 0.95
Ankle PTBW P-FLX CC 0.63 0.31 0.53 0.38
p-Value 0.02 0.30 0.05 0.18
Ankle PTBW D-FLX CC 0.42 0.09 0.44 0.24
p-Value 0.16 0.76 0.11 0.42
Knee PTBW FLX/EXT
ratio
CC 0.36 0.39 0.20 0.43
p-Value 0.23 0.19 0.49 0.13
Ankle PTBW
D-FLX/P-FLX ratio
CC -0.30 -0.37 -0.09 -0.20
p-Value 0.32 0.21 0.77 0.48
Table 4. Pearson correlations between RMSd and other variables under the squat
and the stand conditions for AP and ML direction.
99
Variable Pearson
Correlation Squat AP
Squat
ML Stand AP Stand ML
TPS tibial CC 0.05 0.01 0.24 0.40
p-Value 0.86 0.97 0.41 0.15
TPS plantar CC -0.20 -0.13 0.17 0.00
p-Value 0.52 0.68 0.57 0.99
Proprioception FLX CC 0.00 0.03 0.36 0.30
p-Value 0.99 0.93 0.23 0.33
Proprioception EXT CC -0.25 -0.24 -0.18 -0.13
p-Value 0.44 0.45 0.56 0.66
Knee PTBW FLX CC 0.20 0.14 0.52 0.43
p-Value 0.50 0.64 0.06 0.12
Knee PTBW EXT CC -0.25 -0.48 0.53 0.11
p-Value 0.41 0.10 0.05 0.72
Ankle PTBW P-FLX CC 0.36 0.20 0.68 0.45
p-Value 0.23 0.51 0.01 0.11
Ankle PTBW D-FLX CC 0.07 -0.09 0.48 0.37
p-Value 0.81 0.77 0.08 0.19
Knee PTBW FLX/EXT
ratio
CC 0.55 0.61 0.17 0.39
p-Value 0.05 0.03 0.55 0.17
Ankle PTBW
D-FLX/P-FLX ratio
CC -0.58 -0.61 -0.28 -0.20
p-Value 0.04 0.03 0.33 0.49
Table 5. Pearson correlations between RMSv and other variables under the squat
and the stand conditions for AP and ML direction.
100
Appendix E Correlation Graphs
Correlation Graphs
101
Figure 16. Correlation graphs for COP velocity and TPS.
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Tibial Site (log10)
Touch Pressure Sensation
COPv Squat AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Tibial Site (log10)
Touch Pressure Sensation
COPv Squat ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Plantar Site (log10)
Touch Pressure Sensation
COPv Squat-AP
0
2
4
6
0 2 4 6C
OP
(cm
/s)
Plantar Site (log10)
Touch Pressure Sensation
COPv Squat ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Tibial Site (log10)
Touch Pressure Sensation
COPv Stand AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Tibial Site (log10)
Touch Pressure Sensation
COPv Stand ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Plantar Site (log10)
Touch Pressure Sensation
COPv Stand AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Plantar Site (log10)
Touch Pressure Sensation
COPv Stand ML
AMP
CTL
102
Figure 17. Correlation graphs for COP velocity and proprioception.
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Flexion (Degrees)
Proprioception
COPv Squat AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Flexion (Degrees)
Proprioception
COPv Squat ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Extension (Degrees)
Proprioception
COPv Squat AP
0
2
4
6
0 2 4 6C
OP
(cm
/s)
Extension (Degrees)
Proprioception
COPv Squat ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Flexion (Degrees)
Proprioception
COPv Stand AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Flexion (Degrees)
Proprioception
COPv Stand ML
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Extension (Degrees)
Proprioception
COPv Stand AP
0
2
4
6
0 2 4 6
CO
P (
cm/s
)
Extension (Degrees)
Proprioception
COPv Stand ML
AMP
CTL
103
Figure 18. Correlation graphs for COP velocity and knee muscular strength.
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2C
OP
(cm
/s)
PT-BW Knee Extension (N/Kg)
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
COPV Stand ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
COPv Stand ML
AMP
CTL
104
Figure 19. Correlation graphs for COP velocity and ankle muscular strength.
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2C
OP
(cm
/s)
PT-BW Ankle DF (N/Kg)
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
COPv Stand ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
COPv Stand ML
AMP
CTL
105
Figure 20. Correlation graphs for COP velocity and muscular strength ratios.
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
COPv Squat AP
0
2
4
6
0 1 2C
OP
(cm
/s)
PT-BW Ratio Ankle DF/PF
Muscular Strength
COPv Squat ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
COPv Stand ML
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
COPv Stand AP
0
2
4
6
0 1 2
CO
P (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
COPv Stand ML
AMP
CTL
106
Figure 21. Correlation graphs for RMS displacement and TPS.
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Tibial Site (log10)
TPS Sensation
RMSd Squat AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Tibial Site (log10)
TPS Sensation
RMSd Squat ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Tibial Site (log10)
TPS Sensation
RMSd Stand AP
0.0
0.5
1.0
1.5
0 2 4 6R
MS
d (
cm)
Tibial Site (log10)
TPS Sensation
RMSd Stand ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Plantar Site (log10)
TPS Sensation
RMSd Squat AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Plantar Site (log10)
TPS Sensation
RMSd Squat ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Plantar Site (log10)
TPS Sensation
RMSd Stand AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Plantar Site (log10)
TPS Sensation
RMSd Stand ML
AMP
CTL
107
Figure 22. Correlation graphs for RMS displacement and proprioception.
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Flexion (Degrees)
Proprioception
RMSd Squat AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Flexion (Degrees)
Proprioception
RMSd Squat ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Extension (Degrees)
Proprioception
RMSd Squat AP
0.0
0.5
1.0
1.5
0 2 4 6R
MS
d (
cm)
Extension (Degrees)
Proprioception
RMSd Squat ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Flexion (Degrees)
Proprioception
RMSd Stand AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Flexion (Degrees)
Proprioception
RMSd Stand ML
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Extension (Degrees)
Proprioception
RMSd Stand AP
0.0
0.5
1.0
1.5
0 2 4 6
RM
Sd
(cm
)
Extension (Degrees)
Proprioception
RMSd Stand ML
AMP
CTL
108
Figure 23. Correlation graphs for RMS displacement and knee muscular strength.
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2R
MS
d (
cm)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSd Stand ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSd Stand ML
AMP
CTL
109
Figure 24. Correlation graphs for RMS displacement and ankle muscular strength.
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2R
MS
d (
cm)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSd Stand ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSd Stand ML
AMP
CTL
110
Figure 25. Correlation graphs for RMS displacement and muscular strength ratios.
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSd Squat AP
0.0
0.5
1.0
1.5
0 1 2R
MS
d (
cm)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSd Squat ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSd Stand ML
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSd Stand AP
0.0
0.5
1.0
1.5
0 1 2
RM
Sd
(cm
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSd Stand ML
AMP
CTL
111
Figure 26. Correlation graphs for RMS velocity and TPS.
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Tibial Site (log10)
TPS Sensation
RMSv Squat AP
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Tibial Site (log10)
TPS Sensation
RMSv Squat ML
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Plantar Site (log10)
TPS Sensation
RMSv Squat AP
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Plantar Site (log10)
TPS Sensation
RMSv Squat ML
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Tibial Site (log10)
TPS Sensation
RMSv Stand AP
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Tibial Site (log10)
TPS Sensation
RMSv Stand ML
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Plantar Site (log10)
TPS Sensation
RMSv Stand AP
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Plantar Site (log10)
TPS Sensation
RMSv Stand ML
AMP
CTL
112
Figure 27. Correlation graphs for RMS velocity and proprioception.
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Flexion (Degrees)
Proprioception
RMSv Squat AP
0
6
12
0 2 4 6
RM
Sv
(cm
/s)
Flexion (Degrees)
Proprioception
RMSv Squat ML
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Extension (Degrees)
Proprioception
RMSv Squat AP
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Extension (Degrees)
Proprioception
RMSv Squat ML
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Flexion (Degrees)
Proprioception
RMSv Stand AP
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Flexion (Degrees)
Proprioception
RMSv Stand ML
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Extension (Degrees)
Proprioception
RMSv Stand AP
0
6
12
0 2 4 6
RM
Sv (
cm/s
)
Extension (Degrees)
Proprioception
RMSv Stand ML
AMP
CTL
113
Figure 28. Correlation graphs for RMS velocity and knee muscular strength.
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2R
MS
v (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Knee Flexion (N/Kg)
Muscular Strength
RMSv Stand ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Knee Extension (N/Kg)
Muscular Strength
RMSv Stand ML
AMP
CTL
114
Figure 29. Correlation graphs for RMS velocity and ankle muscular strength.
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2R
MS
v (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ankle PF (N/Kg)
Muscular Strength
RMSv Stand ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ankle DF (N/Kg)
Muscular Strength
RMSv Stand ML
AMP
CTL
115
Figure 30. Correlation graphs for RMS velocity and muscular strength ratios.
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2
RM
Sv
(cm
/s)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSv Squat AP
0
6
12
0 1 2R
MS
v (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSv Squat ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ratio Knee FLX/EXT
Muscular Strength
RMSv Stand ML
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSv Stand AP
0
6
12
0 1 2
RM
Sv (
cm/s
)
PT-BW Ratio Ankle DF/PF
Muscular Strength
RMSv Stand ML
AMP
CTL
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